280 Prof. F. M'Coy on some new genera 



cast from the wide edge of the cup (representing the secondary 

 lamellae), which extend only a short way towards the centre. 



Var. a. crenulata. 



This beautiful variety differs from the ordinary type in the 

 primary and secondary lamellar sulci, particularly towards the 

 edge of the cup, being bent with numerous small angular zigzag 

 flexures (perhaps from alternating projections on their sides). 

 I might have supposed this to have been a small form of the 

 P. elongata (Phill. sp.), if it was not for his reference to Lons- 

 dale's figure (S. S. t. 16 bis, f. 6), which represents a distinct 

 species which I have frequently seen; the lamellae of the present 

 species are also finer, the size smaller, and the form more regu- 

 lar, and the lamellar ridges of the cast never pitted. On the cast 

 the lamellar sulci are regularly alternate in size, except at the 

 strong simple odd one, on each side of which are two or three 

 short ones. 



Very abundant in the fine greenish Caradoc sandstone of 

 Mulock quarry, Dalquorhan ; in the schists of Cyrn y Brain, 

 greenish schists of Llansaintfraid. 



Petraia uniserialis (M'Coy). 



Sp, Char. Corallum rapidly and regularly expanding, oblique, 

 averaging 5 lines in height and width, radiated with about 

 forty-five or fifty lamellar sulci ; average internal casts nearly 

 5 lines wide and 2 lines high, radiated by the deep slits of 

 twenty-five strong primary lamellae (six or seven in 3 lines at 

 the margin) extending to the centre, where they are united 

 and irregularly compUcated ; between each pair of these slits is 

 a row of small, close, irregular, numerous pits (representing 

 papillae of the secondary lamellae), about three in a space equal- 

 ing the distance of the lamellar slits apart. 



. I frequently find this common species confounded with the 

 P. bina (Lonsd.), which in form and size it resembles, but from 

 which it differs completely in the primary lamellae being simple 

 plates extending to the complicated centre, leaving deep slits in 

 the cast, which therefore has but one set of rows of pits instead of 

 two ; while in P. bina these lamellae are replaced by a row of large 

 papillae, leaving a row of large pits in the cast, extending but a 

 little way towards the centre. The secondary row of lamellar 

 papillae (and pits on the cast between the slits) is much smaller, 

 closer and less regular in the present species than in the P. bina. 

 Some of the casts present a depression in the smaller end, into 

 which a process of the solid part of the apex must have pene- 

 trated. Between the lamellar sulci in some damaged specimens. 



