8 The American Geologist. Juiy.isgi 
the beaks; valves of moderate convexity, rather thin, beaks 
placed at less than one-third of the length from the anterior 
extremity, only moderately prominent (their summits rising, 
in adult specimens, about two millimeters above the cardinal 
teeth); hinge of moderate size: the three divergent cardinal 
teeth separated by clefts of subequal amplitude but very deep 
and abruptly excavated in the case of the anterior cleft and 
less so in the posterior: anterior cardinal tooth small, second 
tooth larger and compressed but not sharply so. third large, 
broad, rlattish-topped and feebly channeled or bifid: posterior 
lateral tooth rather large and long; surface marked with 
ordinary concentric growth-lines of which a few, not regu- 
larly spaced, are usually much stronger than the rest. 
Measurements. — Hight45: length 49; breadth 22mm., in an 
elevated example. Fig. 12 shows an example of the more 
elongate form. 
Occurrence. — In No. '■'< and \ of the Belvidere section, south and south- 
wesl of the railway station. Most common near the transition from 
tlie former in the latter horizon. Specimens in the upper pari of I fre- 
quently occur as casts and moulds, while those in the lower pari of •> 
are usually well preserved. 
None of the rather numerous specimens before me show the 
pallia] line or the teeth of the left valve, but one specimen 
shows the posterior adductor-scar to be only faintly im- 
pressed. 
There is considerable variation in the form of this shell. 
In some examples, the bight is equal to only three-fourths of 
the length, the outline in such being subovate; in others, the 
bight becomes full)- equal to the length and the outline accord- 
ingly is more triangular. 
LEPTOSOLEN OTTERENSIS. sp. nov. 
Plate I. fig. •-'. 
Shell compressed, elongated, subrectangular, the bight con- 
tained nearly two and a half times in the length: dorsal and 
ventral margins nearly parallel back of the beaks, and some- 
what convergent anteriorly from them; anterior margin 
rounded, posterior truncate : beaks at about the anterior third 
of the length: valves thin, each presenting a broad, low. and 
gently elevated, distally widening fold, which extends from 
the beak obliquely downward and forward to the antero-ven- 
