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 mark- 

 ing 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 



