A synopsis of the characters of the Carboniferous limestone fossils of Ireland

SYNOPSIS, &c.&c. MOLLUSCA.The MoUusca, or as anatomists more correctly call tliem, the Heteror/anr/liata, include all the sliell-fish, together with several naked groups of little interest to the geologist.The principal divisions of the class are, 1st.The Cephalopoda, which are the most highly organized, active, and rapacious of the entire group, having a distinct head, furnished with powerful horny mandibles, large, perfectly-formed eyes, a rudimentary skull and brain, powerful fins for swimming, and several other pecuharities of structure only found in the Vertebrata, to which they lead by means of the Fishes; the sexes are distinct.2nd.The Gasteropoda, including all the spiral univalve shells, together with some naked groups, but all characterized by having the foot expanded into a disc for walking ; they have also a head, and two eyes, and usually two or four tentacula; sexes distinct.3rd.The Dit/u/ra, or bivalves; those are much less highly organized than either the Cephalopoda, or Gastero- poda, having no head, tentacula, or eyes, and scarcely any powers of locomotion, having no fins for swimming, or disc-like foot for walking; many of the genera are permanently attached to foreign bodies, either by a byssus, or by the substance of the shell ; they are all females.4th.Brachiopoda, or arm-footed bivalves, of which we shall speak more when we come to them.There are, also, the Pteropoda and Tuidcata.1st.We have 6 SYNOPSIS OF THE CHARACTERS OF THE strata from the clialk to the lias inclusive, and the Goniatites, and gigantic Orthoceratites of the older rocks, seeming to have been among the chief carnivorous animals of those periods.They have all nearly disappeared from our seas.Nautilus and Spirula alone remaining to show us the nature of the animals which inhabited the many chambered shells famihar to the geologist.The Siphonifera are in their internal anatomy most nearly aUied to the Gasteropoda ; they differ remarkably from the Dibranchiata in ha\'ing four gills, and only one heart, and most particularly in wanting the internal dorsal lamina, and being covered by an external polythalamous shell, the chambers of which are connected by a siphuncle differing in structure according to the family.The subdivisions of this tribe are so numerous, and would lead us so far away from our subject, that it is better not to notice them. Family OETHOCERATIDJE.Genus Orthoceras. Gen. Ch.-Shell gradually tapering; smooth; siphuncle central.There appear to be several subgeneric types even of the genus as here restricted, the first of those is Orthoceras proper (fig.2), in which the form is straight conic, the section is circular or nearly so, the si- phuncle central or nearly so, and the septa simple and placed at right angles to the long axis of the shell.CARBONIFEROUS FOSSILS OF IRELAND.13 GONIATITES DISCUS.MCoy.(PI.II.fig.6).Sp.Ch.-Discoid, compressed, smooth ; sides flattened, back rounded ; volutions six ; entirely exposed ; septa, dorsal sinus single, acute; dorsal lobe short, rounded; first lateral sinus bifid ; first lateral lobe twice as long as the dorsal lobe, rounded, sides parallel ; second lateral sinus narrow, pointed, mucronate, equal in length to first lateral sinus ; second lateral lobe short, rounded ; marginal sinus very short, acute.This Goniatite belongs to the remarkable little group including the G. Henslowi, G.ci/clolobus, G. mixo- lohux, &c. and which, from the pecuharltles both of septa, and external form, might make a very natural genus.Diameter one inch seven lines ; length of mouth five lines ; width four lines.GONIATITES EXCAVATUS.Pllil.Goniatites excavatus.Phil.Geol.York, and Pal.Fos.Sp.Ch. -Discoid, depressed ; back rounded ; umbilicus large, margin acute ; siuface with fine, branching, curved, transverse striaj ; septa, dorsal lobe short, bifid ; first lateral sinus acute, angular ; first lateral lobe very large, obtusely rounded ; inner margins parallel ; lateral sinus acute.This species is liable to be confounded with the G. reticidatus, but is distinct both by its septa (having the lateral sinus angvdar, pointed, instead of being wide and obtuse, or with a small mucronate point, as in that spe- cies) and in wanting the spiral striatlon : the form too is not so depressed, and the back is more rounded than in that shell.Goniatites FAscicuLATus.M'Coy.(PL II.fig.8).Sp.Ch. --Discoid ; umbilicus very large ; inner whorls partly exposed ; back very convex, broad, crossed by numerous unequal bundles of fine transverse ridges, having a deep retral wave on the back ; the bundles of transverse ridges about their own diameter apart, the intervening spaces being concave and smooth.This beautifully marked species is distinguished from the G. Listeri, to which it is nearly alhed, by the transverse ribs, instead of being simply rounded, as in that species, being formed each of a bundle of tliin, im- equal ridges ; the umblhcus is also smaller, and with a rounded edge ; the margin is phcated by the passage over it of the ridges ; this part bears large tubercles in the G. Listeri, which is a much more common species. Diameter one inch six lines, thickness of last whorl eleven lines.Goniatites Gibsoni.Phil.Goniatites Gibsoni.Phil.Geol.York.Sp. Ch.-Discoid, whorls, five or six, one-third exposed; back rounded; mouth broad, oval, a little wider than long ; whorls crossed by sharp, forked ribs, most prominent at the edge of the lunblHcus.I am not acquainted with the septa of this remarkable little shell, whict In general form, and in the marking of its surface, more closely resembles an Ammonite than the present genus.There are about five or six tm-ns in the spire ; the volutions are convex ; the back broad and rounded ; the radiating ribs rise boldly from the edge of the umbilicus, and, bending slightly forward, branch about the middle of the side into two smaller ones, which pass over the back ; the sui-face between the ribs is perfectly smooth.Diameter four lines, thickness one line.Goniatites intercostalis.Phil.Goniatites intercostalis.Phil.Geol.York.Sp.Ch.-Discoid depressed ; whorls two-thirds exposed ; back broad, obtusely angular in the middle ; sides with radiating ribs, which form distinct tubercles at the dorsal angle ; between these there are coarse spiral striae.D 14 SYNOPSIS OF THE CHARACTERS OF THE I have not as yet seen the septa of this very rare shell ; the back is broad, bounded by an obtuse angle, from whence the sides are concave, exposing rather more than one half of eacli whorl ; the whorls are about four in number, spirally striated, with rather distant, strong, radiating ribs, forming tubercles when they reach the ridge which bounds the back, where they cease.Diameter one inch, thickness seven lines.GONIATITES LATUS.M'Coy.(PL II.fig.7).Sp.Ch.-Globose, back very broad, rounded; mouth transversely elliptical, twice and half as wide as long; umbilicus rounded, angular, very deep, exposing the edges of the preceding whorls ; surface smooth, with a few distant, bent constrictions ; septa, dorsal lobe simple, twice as long as wide, rounded ; dorsal sinus very wide, rounded ; lateral lobe half the length of the dorsal, width equal to the length, acute ; lateral sinus wide, shallow ; surface smooth.This is one of the very few Goniatites of the mountain limestone, in which the dorsal lobe is simple, as in those of the inferior rocks, it resembles the G. Nceggerathii, but is much more globose, and has fewer whorls.Diameter one inch three lines, width of mouth ten lines, length of mouth four lines.Goniatites Listeri.Mart.sp.Ammonites Listeri.Mart.Pet.Derb.-Ammonites Listeri.Sow.Min.Con.-Goniatites Listeri.Phil.Geol.York.Sp.Ch.-Spheroidal depressed ; mouth twice as wide as long ; umbilicus very deep, conical, exposing the angle of the internal whorls ; edge of the umbilicus tuberculate ; surface with distinct transverse striae, or ridges, having a shallow, retral wave as they pass over the broad back ; septa, dorsal lobe bifid, dorsal sinus long, acute ; first lateral lobe very large, rounded ; lateral sinus little deeper than the dorsal sinus ; wide, mucronate, or suddenly pointed.In this species the umbilicus is so large that all the whorls are half exposed, so that the toothed or plaited edge of the umbilicus can be seen all the way ; the back is broad, slightly convex, and transversely striated.Diameter one and a half inches, thickness one inch.Goniatites micronotus.Phil.Goniatites micronotus.Phil.Geol.York.Sp.Ch.-Discoid, depressed, back rounded; umbilicus very small, rounded; surface with delicate, trans- verse, cm-ved striffi ; septa, dorsal lobe very small, acute, first lateral lobe very large, rounded at the extremity, with their inner edges nearly parallel, dorsal and lateral sinus small and rounded.This obscure species is known from the young of G. obtusus and G. striolatus by the small size of the umbilicus, the form of the septa distinguishes it from all the allied species.Diameter one inch, thick- ness six lines.Goniatites mutabilis.Phil.Goniatites mutabilis.Phil.Geol.York.Sp.Ch. -Globose, smooth; innbilicus wide, acute-edged; mouth more than twice as wide as long; back broad, rounded ; constrictions direct.One or two specimens of this simply formed shell have occurred ; the septa have not been seen as yet, nei- ther have I seen any specimens corresponding to Professor Phillips's figure of the adult.Diameter four lines, thickness three lines.CARBONIFEROUS FOSSILS OF IRELAND.15 GONIATITES OBTUSUS.Phil.Goniatites obtusus.Phil.Geol.York.Sp.CIi.-Discoid, gibbous, somewhat compressed, with nearly parallel sides, and broad, obtusely -rounded back ; umbilicus very small ; surface, when well preserved, very finely striated transversely ; stria3 waved ; septa, dorsal lobe small, obscurely bifid, dorsal sinus angular, acute ; first lateral lobe three times the lent^th of the dorsal, oblong, rounded ; lateral sinus wide, mucronatc.This species bears some resemblance to the Goniatites striatus