FAMILY CALYPTRIAD.E CALYPTREA. 155 



SECTION 6. SCUTIBRANCHIA. 



Animal with a foot for crawling. Gills arranged either in regular series or detached fila- 

 ments in a peculiar cavity, which opens in Jront, either on the back or on the left between 

 the edge of the mantle and the body. Eyes variously placed, sometwies on pedicels. Sexes 

 united, so that they can fecundate themselves. Heart traversed by the rectum, and receives 

 the blood from two auricles, as occurs among most of the bivalves. Shell open, shield- 

 shaped, usually without spire, with a continuous margin. 



FAMILY CALYPTRIADJE. 



Animal with its eyes on small dilatations, either at or slightly above the external base of the 

 tentacles. Respiratory organs composed of filaments adhering to the sides of the branchial 

 cavity. Shell cup-shaped, not symmetrical : summit rarely spiral. 



GENUS CALYPTREA. Lamarck. 



Animal with a conspicuous wide head, bifurcate in front, with a marginal band on each side 

 of the neck. Tentacles lateral, distant, very large, triangular, slender at their extremities, 

 with the eyes on a slight dilatation about the middle of their external or posterior margin. 

 Mantle very thin, without lateral tentacles. Foot subcircular, moderate. Branchial cavity 

 very large, oblique from left to right, opening largely in front, and containing a gill formed 

 of long stiff and exsertile filaments. Vent at the extremity of a small tube, floating in the 

 branchial cavity. Shell irregular, conoidal : summit vertical, and slightly posterior. Aper- 

 ture large, circular ; an irregularly rounded projecting rim or partition within towards the 

 summit. 



CALYPTREA STRIATA. 

 r-LATE VII. FIG. 155. a. B. 

 Calyptrea striata. Say, Journ. Acad. Nat. Sciences, Vol. 5, p. 216. 



Description. Shell moderately solid, conoidal. Surface with numerous slightly elevated 

 equidistant radiating lines. Summit smooth, obtusely pointed, subspiral, inclining towards 

 the left side and the posterior end ; the inner partition cup-shaped, and attached by one side 

 to the shorter side of the shell, acutely angulated at the anterior line of junction, rounded 

 behind, and terminating above near the inner apex of the shell : its margin irregular, not 

 continuous. 



Color, greyish; wax-yellow at the summit. Length of base, 0" 8. Height, 0' 5. 



This shell is not common, but has been brought to me from this coast ; farther south, it is 



more abundant. 



20' 



