134 AMERICAN JOURNAL 



plicate, or angulate, tlic appearance presented by the adult 

 only, should be thus described. 



In some of the species, however, these lines, plicoe or 

 carinse, are persistent in the old shell, under favorable cir- 

 cumstances, but in most specimens are not seen. This is one 

 difficulty which has caused the multiplication of synonymic 

 names, generally unavoidably, on account of the scarcity of 

 specimens, known to be from the same locality, for comparison. 



When a specimen exhibits a perfect spire in the adult state, 

 (rare among the Strepomaiidsc^) and the initial whorls are pli- 

 cate or carinate, they cannot be regarded as affording reliable 

 data for specific discrimination. And it is only when these 

 marks extend quite, or more than half way to the body 

 whorl, that the species should be regarded as plicate or cari- 

 nate. Whether species not usually 2:)licate do not in some 

 localities hecome so, from the absence of disturbing influences 

 of the waters, is a question that we cannot as yet definitely 

 decide ; its decision in favor of such occasional development 

 of plicte would effect the validity of many species which are 

 now regarded as established. 



The development of carinaa or tubercles on the body whorl 

 of the adult shells is not nearly so constant a character as would, 

 at first sight, appear to be the case, and several species are in 

 doubt on this account. Generally, however, these may be 

 regarded as more permanent characters when developed on 

 the body than on the spire, as an adult shell is not subject to 

 the same mutations of form as a juvenile individual. 



Of course, the relations of size and texture are applicable 

 to adults only; and then the former is subject to much 

 variation from external influences. Texture is an important, 

 because a tolerably permanent, discriminative guide. 



Color, external or internal, generally, should not be much 

 relied on, nor the presence or absence of bands, or macula- 

 tions ; but in exceptional cases it is venj characteristic, as in 

 P. virtduhim, Anth., for instance. Perhaps color in the 

 interior is a more reliable feature than epidermal or external 

 hues. 



In some species, however, the presence or absence of bands 

 forms a prominent distinctive feature. 



Form, though subject to variation, may be relied on as one of 

 the best characteristics ; the length, number, and the convexity 

 of the whorls, relative size of the aperture to that of the entire 

 shell, shape of the outer lip and of the columella, are all 

 generally reliable. 



To repeat ; in distinguishing a species of Slrepomatidve^ of 

 course the first step is to ascertain whether it is adult. The 

 signs of juvenility are — sharp extremities^ thin texture, j)ftr- 



