420 
PROCEEDINGS OF THE ACADEMY OF 
large arclied opening beneath the umbo. This truncation makes but a small 
angle with the midumbonal slope, the arch beneath which is partly closed by 
the curtain-like deflection of the posterior part of the shell. External surface 
marked by fine radiating ribs, and a few concentric rugse in front of the beak 
and along the anterior terminal expansion. 
Height of shell from beak along midumbonal slope to remotest point of 
ventral border *59 (100); distance from anterior cardinal angle across the shell 
at right angles with posterior truncation *42 (71); convexity of right valve 
•15 (25). 
Localities. —Marshall, Battle Creek, and R. R. Cut, 3 miles North of Napo¬ 
leon, Jackson county. 
Conocarditjm, Bronn. 
Conocardium ? bovipedale, n. sp.—Shell small, very ven^ricose, truncated 
along the umbonal slope, or a little posterior thereto, by a plane nearly verti¬ 
cal to the plane of the valves, but a little inclined posteriorly, thus producing 
a slightly acute plane angle with the external surface. Beak prominent, 
somewhat enrolled and turned forward ; hinge-line anterior, short, convex, 
joining, by a rounded, obtuse angle, the gently rounded anterior angle, which 
curves more rapidly in approaching the ventral margin and the truncation. 
Posterior, truncated side nearly flat, but a little concave, with an arched, 
mactra-shaped opening under the umbo. Convex surface of shell, with 26 
radiating ribs, slightly flattened along their summits, and very fine, sharp, 
undulating, concentric striae, most distinct between the anterior angle and 
the umbo ; the truncated surface with obsolete arched striae. Right valve 
unknown. 
Length along truncating line *30 (100); distance from anterior extremity to 
truncating plane, at right angles with latter *20 (67); convexity of left valve 
•12 (40). 
Locality. —Marshall. 
This species belongs to the group of C. Napoleonense, but may be easily dis¬ 
tinguished by its coarser ribs, greater ventricosity, less flattened marginal 
regions and nearly mesial truncation. 
Posidonomya, Brown. 
Posidonomya Romingeri, n. sp.—Shell of medium size ; general outline about 
two-thirds of an ellipse, the longer axis of which is nearly at right angles 
with the anterior cardinal slope of the shell, and forms an angle of 75° with 
the straight hinge-line, and one of 33° with the midumbonal slope ; greatest 
width of shell a little nearer the (regularly curved) ventral border; region 
behind the beak a little excavated, making the posterior cardinal region 
appear slightly flattened and produced ; beaks elevated above the hinge-line, 
approximated and slightly turned forward. Surface (of cast) distinctly 
marked by continuous equidistant and direct concentric strise. Hinge un¬ 
known. 
Greatest length of shell (over midumbonal slope) *97 (100); longer axis of 
the elliptic outline ’90 (92); greatest width of shell (at right angles with last 
measure ’70 (72); thickness of right valve *20 (21); number of striae in one- 
tenth of an inch, in the middle of the shell 3£. 
Locality. —Marshall. 
Closely imitates in outline P. vetusta, Sow. sp. (Phill. Geol. Yorks. 211, pi. 
vi. 3), but the beak is less projecting, and the concentric furrows are more 
numerous and smaller. 
Posidonomya Whiteana, n. sp.—Shell of moderate size, oblique, with an 
extended, straight, hinge-line, a subalate expansion before, and a rather flat¬ 
tened and extended posterior margin. Beaks little elevated above the hinge, 
incurved, and slightly turned forward. Umbonal ridge much swollen, situa¬ 
ted anterior to the middle of the shell, and making an angle of 66° with the 
