294 THE CARBONIFEROUS SYSTEM. 



that Phillips himself figures a specimen of his Terebratula rhomboidea 

 with a simple mesial fold, we need not be surprised to find the same 

 peculiarity in one of those from Nova Scotia. Indeed, after carefully 

 examining the three examples forwarded by Dr Dawson, I cannot 

 bring myself to believe that they should be specifically separated. It 

 is well known that the same peculiarity occurs with Rhynchonella 

 acuminata; and any one who examines plates 20 and 21 of my 'Mono- 

 graph of British Carboniferous Brachiopoda ' must feel surprised at the 

 immense variability of which some species are susceptible. 



Fig. 93. — BhyncJionella Dawsoniana, Davidson ; nat. size and magnified. 



" Rhynchonella Dawsoniana, n. sp. (Fig. 93, a, b). 



" Shell very small, almost circular, a little wider than long; dorsal 

 valve moderately and uniformly convex to about half its length from 

 the umbone, at which point a very slightly elevated and flattened 

 mesial fold begins to rise, and extends to the front ; the surface of 

 the shell is also either almost entirely smooth or ornamented with 

 from eight to twelve slightly marked ribs. The ventral valve is 

 gently convex, with a wide sinus ; beak small and incurved. Length 

 three and a half lines, width four lines, depth two and a half lines. 



" This small species does not appear to be rare in a black Lower 

 Carboniferous limestone at Lennox Passage, and is not unlike, except 

 in size, certain examples of M. de Verneuil's Terebratula superstes ; 

 but this last-named Permian shell belongs to the genus Camarophoria, 

 while the one under description belongs to Rhynchonella. I have 

 compared it with a number of equally small young examples of Rhyn- 

 chonella pugnus, from which it appears to differ. 



" Rhynchonella Acadiensis, n. sp. (Fig. 94). 



" Shell small, obscurely rhomboidal, about as wide as long ; dorsal 

 valve rather more convex than the ventral, and presenting, when 

 viewed in profile, a regular curve. The mesial fold commences to- 

 wards the middle of the valve, while the surface is ornamented with 

 twelve or thirteen small radiating ribs, of which four or five occupy 

 the surface of the fold. The sinus in the ventral valve is of moderate 

 depth, and the surface is ornamented as in the dorsal valve. The 



