404 J, Hall on Cryptonella, Centronella, Meristella, 
The interior of C. impressa presents a very strong double pro- 
cess below the beak of the dorsal valve, corresponding to those 
in C. Glans-fagea. 
The external form of all the species heretofore referred to 
Centronella is a distinguishing feature, and, when proved to 
accompanied by an internal apparatus so different from that 
of Cryptonella, will serve to separate them from all the allied 
orms. 
As before remarked, it has been mainly upon modifications of 
this internal loop, or the apohysary system, that the separation of 
most of the genera in the family of Zerebraiulide has been 
made. 
In Cryptonella, we observe considerable analogy with ensse- 
leria, where the slender bands of the loop expand and unite i 
19. 
rocesses. 
Fig. 18. Dorsal valve of Rensseleria Suessana, showing the internal P t rig. 
Fig. 19. Longitudinal section of the same, showing the relations of the pe am 
20. Interior of dorsal valve of 2. ovoides.—Fig. 21. Longitudinal section of os 
; ‘ i : n 
a broad plate, which is obtusely or acutely attenuate in : 
and on the ventral side marked by a ridge along the in - 
janction; from which, at the posterior margin, proceeds @S°™ 
