Ci/praa reticulata and Cypriva histrio distinct. 



but thai they also present differences equally striking and constant, 

 must, 1 think, be acknowledged. These differences extend to the 

 neral form, to the shape of the aperture, as well as to the marking. 

 In form the C. reticulata is much broader, more thickened at the 

 sid< attenuated at the extremities, and less convex beneath 



than the ('. histrio. In some specimens of the former, the sides 

 are bo much thickened as to give the shell very much the form of 

 the C. Mauritiana or C. caput-serpentis. This excessive thicken- 

 ing never takes place in the histrio, which in form is nearer the C. 

 mappa than to the species just named. The aperture of the histrio 

 is less curved than in the reticulata, while in the latter the teeth ex- 

 tend farther on the ventral face of the shell than in the former. I 

 have not found the number of teeth to be a very reliable character 

 in this genus, adult specimens of small size having fewer teeth than 

 larger specimens of the same degree of maturity. I do not, there- 

 fore, use this as a distinctive character in the present case ; though 

 in the specimens I have examined, 1 have found the number of 

 th in the histrio to average higher than in the reticulata, 

 1 n the maj kings of the i wo species we find the following constant 

 distinctions, The whitish spots on the back of the C. reticulata 

 usually more distant and isolated, and less inclined to be poly- 

 gonal than is the C. histrio, and the chesnut groundwork which 

 separates them is less interrupted or mottled with minuter white 

 spots or lines. The dorsal line is nearly central, and more or le 

 irregular and undulating in the reticulata, while it is straight, and 

 much nearer the left side of the shell when placed back upwards, 

 in the histrio. In the; latter, there is usually a black slain at the 

 left ol' the Spire, and though 1 have seen specimens of the histrio 



in which this was not apparent, 1 have never seen a reticulata 

 which shewed it. On the other hand, the ventral blotch of the 

 reticulata, which in thai is always more or less visible, (unless that 

 be an exception which I shall soon mention,) is never seen in the 

 ('. histrio. In the latter, the dark spots on the sides are usually 

 less frequent and smaller than in the former, and the under side of 

 a lighter color, more incline, I to flesh-color, or peach* 

 bloom. It may also be remarked, that in the histrio, the dark 

 ads which are found in the earlii rata rowth, are 



