257 



CHAPTER XV.* 



CARBONIFEROUS LIMESTONE FOSSILS, 



Pinna spatula (M'Cqy), 



Desc. Valves very narrow and much elongated, about four times 

 larger than the width of posterior end, very slightly convex 

 except at the beaks, which are pointed and almost cylindrical, 

 the sides gradually flattening as they approach the posterior 

 end, which is subtruncate or slightly rounded obliquely ; car- 

 dinal margin slightly thickened, with the cartilage ridge very 

 close within its edge ; surface perfectly smooth or with very 

 faint laminar lines of growth parallel with the margins. 

 Length of large, rather imperfect specimen 5 J inches, propor- 

 tional greatest width at posterior end about -f^Qj greatest 

 depth j-^o or iIq. 



Fragments of this species might be taken for a Soien, and the 

 S. siliquoides (Kon.) may have some affinity with it, though spe- 

 cifically distinct. The muscular impression is rather large, 

 though superficial, quadrato-reniform, rather behind the middle 

 of the length, and nearer to the cardinal than the ventral margin. 



Specimens of the above large size, rare in the carboniferous 

 limestone of Derbyshire ; specimens about 3 inches long, and 

 slightly more convex, in the carboniferous limestone of Lowick, 

 Northumberland. 



[Col. University of Cambridge.) 



Cardiomorpha orbicularis (M'Coy). 



Desc. Suborbicular ; anterior end moderately large, semicir- 

 cular, compressed ; ventral and posterior margin very convex, 

 regularly curved ; posterior side small, rounded, gradually 

 compressed; beaks very large, tumid, obliquely inrolled to- 

 wards the anterior end, projecting greatly beyond the hinge, 

 nearly over which is the deepest part of the shell ; valves be- 

 coming gradually flattened towards the margins; surface 

 smooth, even ; substance of the shell very thin ; hinge-margin 

 inflected at right angles, forming a cartilage support rather 



* The species in this chapter date fr-orn the ' Annals ' for Sept. 1853. 



R 



