GASTEROPODS 351 
As has already been remarked, shell-bearing opisthobranchs 
are not abundantly represented in number of species in North 
American waters. South of Cape Cod, in muddy bays and well- 
sheltered places, the little shell, Haminea solitaria, may, however, 
often be found in considerable numbers. 
Genus Haminea 
Hi. solitaria. Like all external opisthobranch tests, the shell of this 
species is thin and fragile, and would appear to be of small importance 
to the creature it only partially protects. It is devoid of spire, is 
shining bluish-white, sometimes brownish in color, and is 
marked with revolving grooves, which, being cut across by 
irregular growth-lines, give its surface a faintly decussated 
appearance. The aperture is as long as the shell; the colu- 
mella is incurved. This little species is especially abundant amines 
in shallow water about Vineyard Sound and in Peconic Bay. _ stitaria. 
Genus Bulla 
B. occidentalis. This species, which is found in the waters of 
Florida on all sandy beaches, is a relative of the Northern species just 
described. The shell is larger than that of Haminea solitaria, and has 
a color-pattern of mottled or clouded reddish-brown on a white foun- 
dation. There is no spire; there is a pit in place of an apex; and the 
aperture extends the full length of the shell. To the naked eye the surface 
appears smooth and shining. It is an exceedingly variable species, 
occurring all through the West Indies, but not north of Florida. The 
shores of the keys along the west coast of Florida are often strewn with 
these shells after storms. The animal, like all the shell-bearing opistho- 
branchs, is very large as compared with the shell, and the large mantle 
folds recurve upward, almost completely hiding the shell from view. 
(Plate LXV.) 
B. nebulosa. This is one of the largest and finest species of the 
family Builide. It is found on the coast of California south of San 
Francisco. The shell is much larger than that of either of the Atlantic 
species mentioned above, but very closely resembles them in outline, 
although it is built upon a more generous plan and is more richly 
painted. It is brownish, mottled with white and yellow patches, and is 
very suggestive of certain kinds of birds’ eggs. The animals have a 
greatly extended mantle which almost completely envelops the shell. 
The foot is extremely large, with great wing-like developments upon 
each side, called parapodia. Some species of Bulla have been seen to 
swim by means of the lazy flapping of the parapodia. (Plate LXV.) 
SEA-HARES 
Closely allied to these outer-shell-bearing opisthobranchs is a 
large and important group of tectibranchs, known as “sea- 
