58 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
The thickness is not readily obtainable as the specimens are mostly 
preserved as molds of single valves, but it is proportionally much the 
same as in C. mutahilis. From the small number studied, and from 
the figures given by Hall and Clarke and by Weller, it is evident 
that C. Icnticidaris is almost, if not quite, as variable in its dimensions. 
In fact the two species are closely related, the only marked difference 
being in the smaller size, lentiform shape, and almost total absence of 
fold and sinus in C JenticuJaris; it resembles very closely, and, possibly, 
if there were a large suite of specimens, would be found to be almost 
if not quite identical in shape with the immature specimens of muta- 
hilis. There is one of the t^'pe specimens of Icnticidaris, a brachial 
valve, which shows distinctly a faint flexure on the anterior margin, 
clearly a trace of the fold and sinus although it is so slight as not to 
be noticeable on the body of the shell. The muscular platforms are 
practically the same in both species. In the spondylium of the pedi- 
cle valve the impression of the adductor is distinctly shown in one 
specimen. Its position is the same as in mutahilis but it is relatively 
broader. Considerable variation occurs in the height of the brachial 
platform above the inner surface of the valve. 
Relationship of the Genus. 
The one structure that characterizes the subfamily Meristellinae 
is that "the jugal bifurcations do not enter the spiralia but recurve 
and join near their origin." Schuchert ('97, p. 129) assigns to it seven 
genera, the position of two of which, Pentagonia and Camarospira, is 
doubtful, as the nature of the jugum is not fully known. Both are 
middle Devonian forms. Of the remaining five, one, Dioristella, is 
Triassic, the others are Middle Devonian or lower. ^ In seeking for 
genera which are most nearly related to Camarophorella, two more 
are eliminated by the absence of muscular platforms in either valve, 
Meristella and Charionella. Tr^o remain, Merista and Dicamara, 
to which Camarospira must be added, although the structure of its 
jugum is unknown. 
The jugum is as yet apparently of no value in seeking a relationship. 
In the genera named above, when it is known, it is not in any such 
1 The Meristella incerta of Simpson from the Waverly at Warren, Pa., is probably 
an Athyris, althouisrli his description will not permit generic identification. There is a 
species of Athyris found at that locality which agrees very well with his description as 
far as it goes. 
