LOWER HELDERBERG ROCKS. 377 



BEYRICHIA. 



I HAVE described a species of Beyrichia on page 317 of the second vo- 

 lume of the Palaeontology of New- York, without referring to the autho- 

 rity for the generic name. The species, now constituting a very pretty 

 and well-marked group under this name, were confounded with Agnostcs, 

 till Professor M'CoY discovered that instead of being a symmetrical 

 trilobate crustacean, the lobes or divisions were unsymmetrical, and that 

 the individuals were the separated " valves of a bivalve entromostracous 

 shell". 



The following is the description of Professor M'Cor : 



Gems Beyrichia (MCoy). 



Beyrichia : M'CoT, Synopsis of the Silurian Fossils of Ireland, p. 57. 

 ^gnosttis and Battus, in part, of authors. 



" Shell bivalve, rotun do-quad rate : ventral margin slightly concave ; 

 " ends very nearly equal, obtusely rounded ; sides equal, very gibbous, 

 " deeply impressed by a strong and wide sulcus, which extends from 

 " the ventral margin nearly to the dorsal, giving a bilobed or reniform 

 " appearance to each valve. Sulcus slightly nearer to the anterior end : 

 " within this sulcus, on each valve and close to the anterior (or smaller) 

 " side, is a lengthened oval tubercle, nearly at right angles with the 

 " ventral margin, and reaching about two-thirds the distance from 

 "■thence to the dorsal margin. Surface smooth [or granulose]. 



Beyrichia i^anulata ( n. s.). 



Plate LXXIX B. Fio. 1 a, b, c, d. 



Right valve semielliptical, the anterior extremity scarcely narrower than 



the posterior : hinge-line straight, a little shorter than the greatest 



length across the middle of the shell. Anterior, posterior and ventral 

 f Pal^ontoloot III.] 48 



