152 SYNOPSIS OF THE CHARACTERS OF THE 



This liandsome species is very rare ; the Lisli specimens are identical with those of the Eifel and Devon- 

 shire, but not with the Silurian ones. 



Atrypa BIFERA. Phil. SP. 

 Terebratula bifera. PInl. Pal. Fos. 



Sp. Ch. — Subrhomboldal, very much depressed; mesial fold very wide, shallow; beaks" small, pointed; 

 surface radiated with very niunerous, rounded, much branched stria. 



This species is rather rare. I described it several years ago in a paper to the Geological Society of 

 DubHn (previous to the publication of the Palaeozoic fossils), under the name of Atrypa dichotoma, and subse- 

 quently published a short description of it in a catalogue which I wrote, of my friend the late Major Sirr's 

 fossils. Length seven lines, width nine lines. 



Atrypa canalis. (?) Soiv. sp. 



Terebratula canalis. (Sbr. Sil. Syst. (?) 



A few obscure specimens, from the very bottom of the carboniferous series, have, with great doubt, been 

 referred to this species ; they resemble the Atrypa sacculus, but are rather narrower, and with a deep sulcus 

 from the beak to the front margin. 



Atrypa cojo'ta. Phil. sp. 



Terebratula compta. Phil. Pal. Fos. 

 Sp.Cli. — Obscurely pentagonal, valves nearly equally convex, front truncated; surface with numerous 

 equal, radiating ridges. Length five lines, width four and a half lines. 

 A few obscure and imperfect specimens only have been observed. 



Atrypa cordiformis. Sow. sp. 



Terebratula cordiformis. Sow. Min. Con. 



Sp. Ch. — Cordiform, acuminated; front very much elevated, with about five acute plaits extending half 

 way to the beak ; sides tumid. 



This species is chiefly distinguished from one of the varieties of the A. acuminata, by being more convex 

 or tumid at the sides, and in the length and distinctness of the mesial plaits. 



Atrypa desquamata. Soiv. 



Atrypa desquamata. Sow. Geol. Trans — Terebratula (Atrypa) desquamata. Phil. Pal. Fos. 

 Sp. C/<.— Longitudinally obovate, convex; beak large, prominent; surface covered with deep, narrow, 

 smooth striae, very much branched as they approach the margin. 



This species varies considerably in form, some specimens being nearly square and much flattened ; they 

 are more commonly however as above described ; some specimens have the front slightly elevated, in others it 

 is plane. Length about one inch and an half, width one inch five lines. I have not seen the perforation be- 

 neath the beak. 



Atrypa excavata. Phil. sp. 



Terebratula excavata. Phil. Geol. York. 



Sp. Ch. — Rhomboidal, very gibbous, beak of dorsal valve large, prominent; sides concave ; three very 

 large, angular, mesial plaits, and two on each side. 



This curious species is distinguished by the great size of its plaits, and the concave space on each 

 side of the beak, which is large, prominent, and not much incurved; the mesial elevation is very high, the 

 depth and width being about equal. Length nine lines, width eleven lines. 



