LAMELLIBRANCHIA TA. 
511 
CYTHERODON, Hall. 1873. 
Cytherodon nasutus. 
PLATE LXXV, FIGS. 10-12 ; and PLATE XCV, FIG. 30. 
Cytherodon -, Hall. Twenty-third Ann. Rep. N. Y. State Cab. Nat. Hist. Ex. pi., pi. 14, tig. 21. 1872. 
“ (Schizodm) nasutus, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations : PI. 75, figs. 10-12. 
18S3. 
Shell large, obliquely ovate or sub-rhomboidal; length a little greater than the 
height. Basal margin broadly rounded in the middle and anterior portion, 
constricted near the post-inferior extremity, which is sub-nasute and abruptly 
rounded. Posterior margin obliquely sub-truncate. Cardinal line arcuate, 
declining posteriorly. Anterior end short, sloping very rapidly from the 
beaks and rounded below. 
Yalves convex in the lower and posterior portions, becoming gibbous in 
the middle and umbonal region. 
Beaks at about the anterior fourth, small, attenuate, rising above the hinge¬ 
line. Umbonal slope defined by a flattening of the valve or shallow furrow 
extending from the beaks to the sinus in the basal margin. Post-cardinal 
slope moderately convex, with the margin abruptly descending from the 
umbonal slope to the cardinal line. 
Test thick. Surface marked by fine concentric strife which are sometimes 
aggregated into fascicles. 
Muscular scars distinct. Inter-pallial area in the cast marked by numer¬ 
ous, very small pustules. Hinge thickened, encroaching upon the cavity of 
the beaks, which is excavate in the cast of the interior. Cardinal teeth inter¬ 
locking, situated beneath and anterior to the beaks. There are apparently 
four cardinal teeth in the right valve and five in the left. 
The specimen described is a cast of the interior, and imperfect along the 
basal margin. When entire it has measured about 53 mm. in length and 
about 50 mm. in height. 
In its general form this fossil somewhat resembles several species of Schizodus, 
