Welter — Kinderhook Faunal Studies. 187 



eral more or less conspicuous growth lines which are usually 

 strongest on the pedicle valve. 



The dimensions of a rather large individual are : length of 

 brachial valve 10 mm., and width of brachial valve 10| mm. 

 The corresponding pedicle valve would, of course, have a little 

 greater length with the same width. 



Remarks, As indicated by the types in the University of 

 Michigan collection, two quite distinct shells were included 

 by White in his species Athyris crassicardiaalis. The orig- 

 inal description applies in the main to the commoner one of 

 these two shells which has been described above, and the 

 specific name is therefore retained for this species, but the 

 generic relations of the shell are extremely doubtful. It is 

 almost certainly not a member of the genus Athyria^ but as 

 no better disposition can be made of it at the present time, it 

 is allowed so to remain until its real generic relationships can 

 be determined. 



Because of its deep muscular impression and coMS<*quent 

 thinness of the shell, the pedicle valve of this species is per- 

 fectly preserved less often than the brachial valve. The 

 most characteristic features of the shell are, the peculiar 

 transverse flattening of the brachial valve, the large cardinal 

 process and the posterior position of the maximum breadth 

 of the shell. 



The other shell which was included in this species by 

 White, is a small member of the genus Gleiothyris which will 

 have to be considered separately. 



Cleiothyris hirsuta Hall. 



PL XVI. f. 25-27. 



Shell subcircular in outline, lenticular, the two valves being 

 subequally convex. Pedicle valve most convex towards the 

 beak, the beak incurved so as to bring the foramen nearly 

 in line with the margin of the shell. Brachial valve regularly 

 convex, its beak closely incurved beneath the beak of the 

 opposite valve. Fold and sinus usually absent, but in some 

 specimens there is a faint sinus in the pedicle valve with a 

 corresponding fold in the brachial valve. Surface of entire 

 shell marked by fine, concentric, lamellose lines of growth, 



