CLAPP AND SHIMER: SUTTON JURASSIC. 433 
somewhat more broadly depressed causing a less angular junction of 
the two valves at this place. The general proportion in the older 
part of the shell is similar. 
Myophoria suttonensis n. sp. 
PI. 41, fig. 12-14. 
Shell trigonal, inequilateral with rounded anterior, and produced 
and angular posterior margin. Breadth and height about equal. 
Beaks situated slightly anterior to middle. Surface marked with a 
radial ridge extending from the umbos to the posterior border, sepa- 
rating from the rest of the shell the posterior dorsal area which bears 
a different ornamentation. Main body of shell ornamented with 
from 17 to 19 radiating ribs; these ribs are much broader than the 
interspaces and are broadly rounded on top; they are strongly but 
minutely crenulated by crowded concentric striae. In the sinus 
bounding the radial ridge anteriorly there are two smaller radial 
ribs; from there, however, the ribs at once become strong and promi- 
nent and thence slowly decrease in strength toward the anterior 
portion of the shell where they become very weak or are wholly 
absent. Numerous concentric striae are prominent upon the ribs, 
but become especially strong at the anterior margin. The radial 
ribs are much smaller on the umbonal area where they are crossed 
by three or four Trigonia-like, strong, transverse ridges. 
Posterior dorsal area nearly smooth. The ornamentation consists 
of concentric growth lines, most prominent over a broad, low medial 
rib. 
Cardinal teeth typical of other Myophorias, — that is, two in the 
right valve, with vertical striations upon their outer and inner edges. 
These fit into corresponding socket-like teeth on the left valve, that 
are striated only upon their inner edges. 
Named after the formation. 
Comparison. — Closely similar to M. goldfussi Miinster ih the group 
of M. costata, a group which, as given by Waagen in Die Lamelli- 
branchiaten der Pachycardientuffe ^ is characterized by "numerous, 
rather blunt, radial ribs and thick, often sharp, concentric growth 
lines." 
• L. Waagen. Die Lamellibranchiaten der Pachycardientuffe der Seiser Aim. Ab- 
handl. k. k. geol. Reichsanstalt, Wien, 1907, vol. 18, pt. 2, p. 146. 
