MUSEUM OF COMPARATIVE ZOOLOGY. Qk 
usual brown or yellow markings; have the umbones of a deep pink, fading off 
on the dome of the valves, and a little more elevated than in specimens from 
shallow water; they do not exceed 15.0 mm. in height, and may be considered 
as forming a variety sybariticum. 
Famity ISOCARDIIDA. 
Genus ISOCARDIA Lamarck. 
Suscenus MEIOCARDIA H. & A. Apams. 
Meiocardia Agassizii, n. s. 
Shell subquadrate, widest at the gently arched base, polished, moderately 
inflated, whitish or yellowish; beaks small, incoiled away from the hinge 
margin, with a depressed but not circumscribed area in front of them; from 
the beak proceeds a strong but moderately sharp-edged keel to the lower 
posterior end of the shell, which is produced in a rather sharp angle; on the 
posterior area thus separated near its inner edge is another keel, less sharp, 
which extends from the beak to the somewhat rounded upper posterior angle 
of the shell, from which the margin obliquely descends with a slight con- 
cavity first, and then a little convex, to the lower angle; between the two 
keels and nearer the anterior one is a single rounded rib extending to the 
margin, over which the concentric sculpture is continuous and unmodified; 
the entire surface is sculptured with fine even concentric ruge, somewhat obso- 
lete toward the umbo and a little stronger behind the principal keel; toward 
the margin are occasional impressed lines indicative of changes in the rate of 
growth and presumably varying with the individual; the anterior end of the 
shell descends toward the base, where it is somewhat pointedly rounded, and 
from which the base extends in an easy outward curve to the posterior angu- 
lation; pallial line faint, simple, margin of the shell plain; hinge much as in 
M. vulgaris Reeve, the cardinal tooth in the right valve rounded behind, gently 
indented on each side; ligament external, in a groove with raised edges, con- 
tinued under the beak as in other species. Lon. of shell 22.0; max. alt. 17.0; 
diam. of right valve 8.0; of whole shell, probably 16.0 mm. 
One right valve dredged off Trinidad by the U. S. Fish Commission in 117 
fms., bottom temperature 64°.5 F. 
The great interest attaching to this species, not only on account of its ap- 
pearance in a new faunal region for the genus, but on account of the very 
small number of recent species known, has led me to insert it here, though not 
obtained by the “Blake.” It is dedicated to the memory of my teacher, the 
late Prof, Louis Agassiz, whose work in the molluscan subkingdom is familiar 
to all. “ Cypricardia” isocardioides of Deshayes (Inv. Bas. Paris) would, from 
the figure, fall into line with M. Agassiz. It is certainly not a Cypricardia. 
