GASTEROPODS 363 



The shells are nacreous within, and the animal, with its rows of 

 waving cirri upon each side, is very suggestive of Trochus. 

 They are, for the most part, shallow- water or littoral forms. 



GENUS Turbo 



T. castaneus. This species has a range as far north as Cape Hatteras, 

 and is especially abundant at Tampa, on the west coast of Florida. The 

 peculiar operculum is sufficient to identify the genus at once. One 

 variety of this species has a crenulated shoulder upon the body-whorl 

 and is referred to as Turbo crenulatus. A series of intermediate 

 forms establishes the specific identity of the two varieties. (Plate LXVII.) 



FAMILY 



The Neritidce are strictly littoral forms, almost entirely confined 

 to the warmer waters of tropical seas. The animal preserves the 

 usual diatocardian features has a short snout and long tenta- 

 cles. Unlike the trochids and Turbo, it has no cirri along the 

 epipodial margin. The shells are peculiarly shaped, the spire 

 being greatly flattened and scarcely noticeable on account of the 

 unduly large development of the body- whorl ; thus the shell takes 

 on a decidedly patelliform appearance. It is without an umbilicus. 

 In the principal genus Nerita the outer lip is sharp on the edge, 

 but greatly thickened just within. 



GENUS Nerita 



N. peleronta. This shell has two teeth on the wide, flat columellar 

 lip, and about them is a blotch of red, suggesting blood. The common 

 name of this shell, " bleeding-tooth, 1 ' is very appropriate. Found in 

 southern Florida. (Plate LXVII.) 



N. tessettata is a smaller species, with heavy revolving ribs, and is 

 further decorated with transverse oblique black lines. The operculum 

 is calcareous. Both of these species have the habit of absorbing the 

 entire inner portion of their shells. They belong to the West Indian 

 fauna, and occur in great numbers on rocky or coral shore stations. 

 They also may be found on the east Florida coast, well to the south. 

 A third species, N. versicolor, often occurs, associated with the other 

 two. It is somewhat smaller than the others and can easily be distin- 

 guished by the four teeth on the columellar lip, the edge of the 

 columella being convex. (Plate LXVII.) 



GENUS Neritina 



The genus Neritina is very closely allied to the last, having 

 quite the same form of shell ; but it is usually more globular and 



