80 AMERICAN JOURNAL 



less sufficient material upon which to base his description and 

 figures, and I do not desire to impugn his statement on such 

 slender material as that before me. Still it would have been 

 satisfactory to have been able to confirm it.* 



Several casts of what must be supposed to be the neural (ven- 

 tral) or long beaked valve are before me. They are from the 

 Guelph limestone of Canada. They appear to represent a spatu- 

 late or spoon-shaped shell, with an acuminated beak. The car- 

 dinal border is transverse (though slightly irregular) rather promi- 

 nent and with an anterior convexity in the median line. The 

 beak has a well defined, somewhat depressed, false area, with a 

 rounded ridge on each side of it extending to the hinge-line. On 

 each side of this ridge is a broad shallow gutter, between the 

 former and the edge of the beak. The hinge line being very 

 much arched, this groove is continued on each side, some little 

 distance anteriorly outside of and beyond the most transverse 

 portion of the hinge line. Over the whole of the beak are strong 

 transverse rugae or striae of growth, which are especially promi- 

 nent upon the area, but which are readily traced over the 

 ridge and groove to the extreme edge of the beak at the 

 sides. The margins of the valves appear to have been wide and 

 thick as in Crania, but smooth. The beak somewhat resembles 

 that of Obolas, or less that of Aorotreta, in its plane aspect. No 

 subapical pit exists in the American fossils. 



I am inclined to suspect that these shallow areal gutters are 

 what have been considered as sockets or grooves for the insertion 

 of the edge of the haemal (dorsal) valve by Dr. Lindstrb'm. After 

 careful examination of his specimen, I fail to find any grooves 

 on the lateral margins of the neural valve, such as he figures. 

 On the contrary, these, are very wide, flattened and smooth. 

 That in the American species these gutters cannot have served 

 such a purpose is evident, for they are strictly confined to the 

 lateral extensions of the area which was not opposed to any part 

 of the opposite valve. The area, as noticed by Mr. Billings, is 

 at an obtuse angle to the plane of the margin of the valves in 

 most specimens. 



The hollow processes, as indicated by the casts, differ consid- 



* It is possible that the processus cardinalis of Lindstrom may be, 

 with the supposed cardinal pit, due to erosion of the much incurved beak 

 of the hremal valve, reciprocally with that part of the area opposite to it, 

 in the neural valve, such as is occasionally seen in the opposed beaks of 

 bivalves. 



A note from Mr. Davidson confirms the existence, in some specimens, 

 of a depression on the hinge-margin of the Gotland shell and a corres- 

 ponding convexity in the dorsal valve, while corroborating my supposition 

 in regard to the absence of the marginal grooves, as figured by Lindstrom. 



