176 FISSURELLA. 



alone support it. Surface radiately ribbed. Orifice long, narrow, 

 dilated in the middle, bordered inside by an oval callus which is 

 not truncated posteriorly. Edges crenulated. 



The animal has been figured by A. Adams (Genera Rec. Moll.) 

 and by Dr. Fischer (Journ. de Conchyl. vi, pi. vii). The former 

 author has unquestionably made a mistake in the species ; his figure 

 does not represent Clypidella pustula. This blunder has mislead 

 most subsequent investigators, causing them to give the group 

 higher systematic value than its characters warrant. Fischer's 

 figures show the animal to be very similar to the other species of 

 Fissurella, comparatively small, and wholly covered by the shell, 

 except the projecting head. 



The animal with shell is shown on pi. 59, fig. 42 ; in fig. 43 it is 

 seen from above with the shell removed ; fig. 44, ventral aspect of 

 the same. It is, says Fischer, quite flat, and in the contracted con- 

 dition the free borders of the mantle do not extend to the edge of 

 the shell by several millimeters ; in the living state it is expanded, 

 its fringe corresponding to the sinuosities of the shell-edge, but not 

 reflexed up over the shell, which has epidermis and is often covered 

 all over with marine incrustations. The mantle-edges are double, 

 ornamented with little tubercles ; the upper edge is very regularly 

 crenulated, corresponding with the depressions in the edge of the 

 shell ; the lower edge has fine papillae throughout its length. Anal 

 orifice oval, elongated, pretty large, membranous ; its edges not 

 digitated nor formed into a siphon ; muscle-impression extending far 

 forward, narrow, rounded at its anterior extremity. The two ends 

 are united by a narrow, horizontal transverse muscle band, lacking in 

 other species. The head is robust, elongated, extending in front 

 of the shell when alive. Tentacles thick and short ; mouth forming 

 a vertical slit. Foot exactly oval, a little wider behind, quite thick, 

 perceptibly rugose above, but not having tubercles large enough to 

 be seen on a design of natural size. Epipodial row of tubercles 

 present. 



F. PUSTULA Lamarck. PL 59, figs. 42-47. 



Shell rounded-oval, depressed, truncated in front ; margin sinuous, 

 elevated in. front and behind; orifice cross-shaped, situated at the 

 front third of the shell, bounded by a red line. 



The outline is oval, more or less truncated in front, much de- 

 pressed, the altitude contained about four times in the length. 

 The color is usually buif with short red rays around the perforation, 



