250 SHELLS AND SHELL-FISH. PART I. 



by the fishermen. The head and lips are much like those 

 of a slug ; and the lower tentacula, which are flattened, 

 are small, and placed on the edge of the lower lip, 

 while the eyes are situated above them ; the branchia 

 are composed of complicated lamellae, placed on the 

 back, but covered by a small membraneous mantle, in 

 which is a thin, convex, and horny plate, hardly to be 

 called a shell, since it more resembles an operculum. 

 The edges of the foot, which is enormous, forms around 

 it a prominent margin or crest, so dilated that they can 

 be thrown over the back, just like the mantle of the 

 cowries and the Bullce ; and with these processes the 

 animal occasionally swims. "An enormous mem- 

 braneous crop," observes Cuvier, " leads to a muscular 

 gizzard, armed internally with cartilaginous and pyra- 

 midical processes, which is followed by a third stomach, 

 provided with sharp hooks ; and this again by a fourth, 

 in the form of a ccBcum." These animals appear to 

 feed only on sea-weed, and are oviparous. Such are 

 the characters of the typical AplysiancB, but there are 

 several exceptions. In the genus Aplysia Linn., the 

 body is excessively thick, and the lobes so large that 

 they can be used for swimming : but in Thallepus* 

 Sw., the form is much more slender, the lobes shorter, 

 '^' the eyes not visible," and the lower pair of tentacula 

 wanting. Dolabella, according to the published figures, 

 is pear-shaped ; the broadest part, which is rounded, 

 being posterior, where there is an oblique disk, and a 

 hatchet-shaped shell which covers the branchia. The 

 next genus, Bursatella, is still shorter, so as to become 

 nearly globular ; and the edges of the mantle are united 

 over the back, so that there is merely a passage for the 

 water to pass to the gills. The fifth genus, Notarchus, 



* Thallephs ornatus Sw. A most beautiful figure of a species to which 

 I give this name, is among Guilding's drawings, but without any descrip- 

 tion ; it was evidently finished from the living animal. Thegeneral colour 

 is sea green, covered with minute black and white dots ; the edges or crests 

 of the reflected mantle have a broad edging of the richest orange, bordered 

 on their outer edge with a line of deep black ; the tentacula are also 

 orange, and formed like those of Aplysia. Total length about S^ in. The 

 only memorandum on the drawing is, " eyes not visible :" whether this had 

 any covering over the branchia I have no means of judging. 



