129 



ance with that of Centronella as described and illustrated 

 in the Canadian Naturalist and Geologist, Vol. IV, April 1859. 



Through the kindness of Prof. Winchell, I have been 

 put in possession of some specimens of this species, with 

 parts of others illustrating the internal structure, together 

 with drawings representing the loop. 



An examination of the external characters shows that 

 the shell has the form and texture of Cryptonella. " Both 

 valves with regular lens-like convexity, shell obsoletely 

 striate concentrically, and having a minutely punctate 

 structure." The form and other characters of the cast are 

 like that of species referred by me to Cryptonella. In the 

 ventral valve are two delicate, slightly curving dental la- 

 mellae, which are shown in casts by a narrow slit on each 

 side of the beak. " The casts exhibit on the ventral side a 

 delicate impressed line extending from the beak to the mid- 

 dle, and on the right and left of this a fainter one ; on the 

 dorsal side, a median impression, with two fainter ones on 

 the right and two on the left." These characters appertain 

 to the casts of Cryptonella (see fig. 9), as shown in the 

 ventral side of large individuals ; having three defined, 

 slightly impressed spaces, limited by narrow lines which 

 extend to the middle of the shell, below which there are 

 sometimes vascular impressions visible. 



On the dorsal side we have the median impressed line 

 with two fainter ones on each side, which, in seme condi- 

 tions of preservation are obscured by the muscular impres- 

 sion ; and below these are frequently seen diverging vascu- 

 lar impressions 



The internal loop of Cryptonella julia, illustrated from 

 drawings of Prof. Winchell, is shown in figures 1 and 2, 

 which are four times enlarged, and are thus described : "A 

 delicate ribbon-like loop originates from the stout blunt 

 crura on each side of the socket-valve, having its flat sides 

 at first vertical ; the two branches of the loop proceed at 

 first in lines parallel or a little convergent, and then grad- 



