Neio LameUihranchiata. — Illrich. 103 
fourths as long as the shell, terminating abruptly where it joins 
the concave posterior edge, with the upper part of which it forms 
an angle little short of 90°. Anterior end a little the widest, 
strongly convex, especially above ; below rounding neatly into the 
at first gently convex, then straight and finally concave liasal line. 
Posterior ridge thin but very prominent, curving slightly in its 
course from the beak to the sharply produced postero-basal angle. 
Surface uniformly convex, and marked with fine, thread-like con- 
centric lines in the antero-basal three-fifths, beyond which it first de- 
scends into a sulcus and then ascends sharply into the ridge, drop- 
ping on the other side even more abruptly into the wing-like pos- 
tero-dorsal part of the shell. On each side of the posterior ridge 
there are distinct divaricating lines, twice as strong as the con- 
centric lines on the anterior part of the shell. They join each 
other on the ridge, and, those on the lower side of the latter, the 
concentric lines at angles of about 70°. Finally, there is another 
set of such lines along the dorsal edge, running parallel with the 
set on the lower side of the ridge. Internal characters unknown ; 
shell substance very thin. 
Length 12.5 mm., hight at the beaks 5.8 mm.,hight at posterior 
end of hinge 5.1 mm., greatest thickness of closed valves 4.1 mm. 
Casts of the interior would be distinguished by having the dor- 
sal and ventral margins more nearly parallel than is the case in 
any of the other species referred to the genus. With the shell in 
a good state of preservation the species is distinguished from all 
Silurian lamellibranchs by the peculiar surface ornamentation. 
Formation and locality: Near Cannon Falls, Minnesota, in the 
"Phylloporina bed" of the Trenton shales. 
Tellinomya longa, n. sp. 
Plate vir, Figs. 17 and 18. 
Shell small, compressed, elongate, elliptical, the length equalling 
a little more than twice the greatest hlght. Beaks small, situ- 
ated about one-fourth of the entire length from the anterior ex- 
tremity. Cardinal line, on the whole, very sligiitly convex, 
straight behind the beaks; anterior end short, semi-circular; 
ventral margin gently convex; posterior end a little narrower than 
the anterior, and more sharply rounded. Surface with ol)seure 
concentric lines; sloping rapidly at the cardinal margin l)ut 
very gently to the ends and ventral edge. Hinge plate of mod- 
erate strength, bent a little beneath the beak, and with a thiekcn- 
ino- on the lower side in front of same. Posterior to tlie l»e:ik the 
