174 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
directions, many curved back on the shell, nearly every one 
with a double curve, and all in motion. These are glassy in 
appearance and marked with white dots. Their ends are slant- 
ingly truncate and under a fairly high power brown pigment 
markings are seen which are supposed to be ocular in function. 
A transparent fold of the epithelium with two tufts of cilia 
terminate the ends of these graceful appendages (Fig. 28, a and 
6). The foot is long, white and pointed and active in its move- 
ments. The syphons, short as they are, stretch down to the 
bottom of the dish and push the shell about. After jumping 
in this way the syphons contract within the shell but the ocular 
tentacles remain expanded. The foot is also active in shoving 
the shell about. Within the shell at the base of the branchial 
tube is a lappet or shield as described in certain European 
species of Cardium. This lappet is apparently suspended from 
the upper wall of the branchial tube. It lies transversely to 
the longitudinal axis of the body. It is tough, opaque, and non- 
contractile. I know nothing homologous to this curious struc- 
ture in other lamellibranchs. Eggs were discharged in mucous 
masses in the latter part of July. 
APHRODITE GROENLANDICA (Gmelin). 
Fig. 29. Length, 76 mm. 
Fio. 29. — Aphrodite groenlandica (Gmelin). 
