4-36 Cypnca reticulata and Cyprrea hislriv distinct. 



but that they also present differences equally striking and constant, 

 must, I think, bo acknowledged. These differences extend to tlio 

 general 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 

 sides, less attenuated at the extremities, and less convex beneath 

 than the C. histrio. In some specimens of the former, the sides 

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

 the C. Mauritiana or C. caput-scrpentis. 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 thehistrio 

 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 tn 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, I have found the number of 

 teeth in the histrio to average higher, than in the reticulata. 



In the markings of the two species we find the following constant 

 distinctions, Tin; whitish spots on the back of the C. reticulata, 

 are 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 less 

 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 stain at the 

 left of tho spire, and though I have seen specimens of the histrio 

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

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

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

 bo an exception which I shall soon mention,) is never seen in tho 

 O. histrio. In tho latter, the dark spots on the sides arc usually 

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

 tho shell is of lighter color, more inclined to flesh-color, orpeuch- 

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

 transverse bauds which are found it) the earlier stage of growth, are 



