SILURIAN RADIATA. 165 



in collections as Cyathophyllum turUnatum, to which it bears some 

 superficial resemblance, but has no real specific or even generic 

 relation. 



Very abundant in the Coniston limestone of Coniston ; in the 

 calcareous flags of Applethwaite Common ; fine sandstone of 

 Mulock quarry, Dalquorhan; flags of High Haume; slates of 

 Llansaintfraid. 



{Col. University of Cambridge.) 



Petraia suhduplicata (M^Coy). 

 Sp. Char. Regularly conic, slightly oblique and curved at the 

 tip ; outer wall thick, marked with one or two small interrup- 

 tions of growth, and with fine, longitudinal, distant impressed 

 equal striae (seven in 2 lines, at a diameter of 5 or 6 lines) ; 

 average length 9 lines, of which the 3 lines nearest the apex 

 are filled with solid calcareous deposit ; width 7 lines. Casts 

 regularly conic, subtruncate at small end; length and width 

 about equal, regularly sulcated by twenty-seven to twenty- 

 eight strong, straight, primary lamellar sulci extending to the 

 centre, where they are irregularly complicated into a large cel- 

 lular mass ; between the large slits are an equal number of 

 finer ones, extending about three-fourths the length of the 

 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 diff*ers 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 lamellse 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 sandstone of Mulock 

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

 schists of Llansaintfraid. 



{Col. University of Cambridge.) 



Petraia uniserialis (M'Coy). 

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



