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The interior is marked by large, double, profoundly deep
muscular impressions; the principal scars are abruptly de-
pressed on the inner margins, the minor scars faintly marked
except on old individuals. The hinge plates are of medium
width and contain about eight or ten slightly curved teeth on
the anterior side of the beak, and from twelve to fourteen on
the posterior side; beaks (in the cast) rather distant. The
internal cavity of the shell is deep.

This species somewhat resembles T. contracta (Clenodonta
contracta, Salter, Canadian Organic Remains, Decade I, pl. 8,
fig. 4 and 5); but differs in the greater proportional length,
greater breadth of the anterior end, and greater obliquity of
the posterior slope. The shell is more ventricose, the beaks
nearest to the posterior end (instead of the anterior) and the
muscular impressions more deeply marked.

Geological Formation and Locality. In rocks of the age of
the Trenten limestone group; the buff limestone, at Beloit,
Janesville and Mineral Point, Wisconsin; at Dubuque, Iowa,
the Falls of St. Anthony, and other places.

Collectors. Prof. Nason, E. Hobart and James Hall.

TELLINOMYA OVATA (n.s.)

Description. Shell ventricose, sub-ovate; cardianal line straight
or very little curved; anterior and broad, obliquely truncate;
posterior end short, narrow; basal margin broad rounded, a line
drawn from its junction with the anterior and posterior slopes
passes across the middle of the shell; beaks small, not promi-
nent, curved, directed towards the anterior end. Valves gibbons
at the anterior and attenuate at the posterior end; the length,
breadth and thickness of the valves when compared are seven,
six and five. Surface of shell smooth or marked by a few con-
centric lines of growth of moderate strength.

This species resembles T. nastula; but the beaks are more
nearly central, and the posterior end is not produced in
the same manner. The basal line is regularly curved and does
not show the contraction on the posterior side of the middle of
the base which is observed in that species.

Geological Formation and Locality. In the Trenton group,
(Buff limestone,) Beloit, Wisconsin.

Collector. Edward Daniels.