marine British Shells and Animals. 185 
tracting the upper lamina, as represented in the annexed figure : 
the front is formed into a bifid process, like two angulated ten- 
tacula: behind, originating from the base of this, are two ten- 
tacula of a sub-cylindric form, truncated at the end, canalicu- 
lated beneath, and uniting towards their base: eyes two, very 
small and black, placed contiguous at the base of the tentacula: 
the plumous appendage on the right side originates near the 
head immediately behind the foramen. In one instance a cylin- 
dric proboscis was observed to be protruded half an inch in 
length, but the animal died with it retracted : the genitals of one: 
specimen were also very evident immediately before the lateral 
foramen, and appeared slender, and sub-spiral, as in the common: 
garden snail. Diameter of the largest upwards of two inches. 
The shell, or Bulla membranacea, Tab. XIL. fig. 4. is sub-mem- 
branaceous, ovate, and greatly depressed, with a minute lateral 
volution. It is nearly allied to Bulla plumula, butis more mem- 
branous, rather more convex, the small volution and apex more 
prominent, and not placed so lateral: it is wrinkled concentri- 
eally, and covered with a silvery epidermis tinged with pink, 
changeable in different points of view, occasionally appearing. 
nacred or metallic. As the shell dries it usually cracks about 
the margin, which is extremely delicate; and the contraction of 
the epidermis gives it a more wrinkled appearance. The size of 
the largest shell taken is nearly an inch and a half in pees 
and an inch in breadth. 
It is remarkable that this very iul animal, ud highly in- 
teresting shell, should have evaded the researches of naturalists so. 
long, especially as they are of considerable magnitude. Proba- 
bly however the shell, independently of the animal, would never 
have come to light, since it appears to be too delicate to bear the 
agitation of the waves upon the finest sandy shore. Dissection of 
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