and allied Brachiopod genera. 405 
der process in the ventral cavity. We may readily conceive of 
this central longitudinal ridge or carina, along the cicatrix of the 
two parts, being produced into a thin vertical plate, projecting 
backwards in the line of the process from the base of the con- 
joined lamellz in Aensseleria, when it would much resemble 
the median plate of Cryptonelia (see figures 18, 19, 20 and 21 
From the data here given, it will be seen that the genus Cryp- 
tonella is nearly related to Centronella; differing in the external 
form of the typical species, and in some features of the cast. 
Since the preceding observations were printed, I have received 
from Dr. Rominger a figure illustrating t : 
interior of Centronella Glans-fagea, as ob- 
served by him (fig. 22). Admitting the 
identity of the species, this figure of the 
loop is quite different from that given by 
Mr. Billings for Centronella Glans-fagea ; 
and shows essentially the same character 
as that of Cryptonella. Should this internal 
structure prove to be the true structure of Centronella Glans-fagea. 
Centronella, the minor differences inted Interior showing the loop, 
out in the form of the shell and of the cast, from. Dr. C. 
between Céentronella Glans-fagea and au- Pomisger. 
thentic Cryptonella, are scarcely sufficient to establish generic 
distinctions, 
At a later date however,’ Mr. Billings has published Ceniro- 
nella Heeate, giving, in fig. 99a “a specimen with the dorsal valve 
temoved, showing the loop which is covered with minute crys- 
tals of silex.’’ In this species, having all the external characters 
of a congener of ©. Glans-fagea, no indication is given that any 
difference had been observed in the character of the loop, from 
that published in 1859. 
or for reference to existing genera, are yet exhausted, among 
the Terebratulide of the Upper Silurian and Devonian rocks, 
* Canadian Journal, May, 1861, p. 272. 
Am. Jour. Sct.—Seconp Sentrs, Vou. XXXV, No. 105.—Mar, 1863. 
52 ; 
