xlvi 
SYNOPSIS OF GENERA. 
external ligamental cicatrix or lunule, which are always marked features in the 
Grammysidae. Some of the species referred to this genus by American authors 
will ultimately be referred to other genera. 
Examples: Orthonota undulata, pi. lxxviii, figs. 37-42. 
Orthonota carinata, pi. lxxxiii, figs. 34, 35. 
Palseosolen, n. sub-genus. [Type, Orthonota siliquoidea, Hall.] 
Shell equivalve, very inequilateral, extremely elongate, solenoid. Dorsal and 
ventral margins sub-parallel. Anterior end short, rounded at the extremity. 
Posterior end elongate, extremity truncate, gaping. Beaks sub-anterior, small, 
appressed. Cardinal line straight. Umbonal slope prominent and extending 
toward the post-basal extremity. 
Surface marked by concentric striae of growth. 
Hinge characters and teeth unknown. Ligament apparently internal. Mus¬ 
cular impression and pallial line undetermined. 
Surface (of the cast) marked by the remains of fine striae of growth. 
The only species known has the general aspect of Orthonota, but the surface 
is smooth with the exception of the striae of growth. The posterior end is 
gaping and the anterior margin has the appearance of being slightly reflexed. 
Example and type: Palceosolen siliquoidea, pi. lxxviii, fig. 33. 
Cypricardinia, Hall (Palaeontology of New York, vol. iii, text, p. 266. 
1859. Prelim. Notice Lamellibranchiata, 2, p. 81. 1870). 
[Type, Cypricardinia lamellosa, Hall.] 
Shell inequivalve; the right valve the more convex, very inequilateral; 
sub-rhomboid, obovate or sometimes trapezoidal, wider posteriorly. Anterior 
end short, declining from the beaks and rounded below. Posterior end wider 
and obliquely truncate. Beaks sub-anterior, incurved and appressed. Umbo 
of the right valve often prominent. Cardinal line straight or arcuate, rising 
from the beaks. Umbonal slope prominent, often obtusely angular. 
Surface marked by strong, concentric, lamellose undulations, with interme¬ 
diate fine striae of growth, and in some species by radiating striae, which are 
