318 UNITED STATES GEOLOGICAL SURVEY OF THE TERRITORIES. 



inner lip in the living typical species, nearly straight and somewhat callous; 

 surface smooth or striated, and, in recent examples, covered with a dark 

 gamboge-colored epidermis ; operculum corneous, subspiral. 



This group seems to be nearly related to Amaura, Moller, and may even 

 be found not to be more than subgenerically distinct when the fossil species 

 are more carefully compared with the living typical forms. At any rate, there 

 are a number of Cretaceous and Jurassic species that seem to stand, as it 

 were, intermediate between the two in form. Looking at the very few 

 known living species of these two types, the most observable differences in 

 the shells alone, consist in the more elevated spire, shallower suture, thinner 

 inner lip, and entirely imperforate columella of Amaura. It should be 

 remembered, however, that but a single species of the latter and some two 

 or three of Amauropsis are known among our existing Mollusca, while in 

 groups containing many species, even more marked differences are sometimes 

 not considered of generic value. 



The genus Amauropsis, as here understood, appears to have been 

 represented at least as far back as the Jurassic epoch ; and a number 

 of Cretaceous so-called Naticas seem to belong to it-. In the Tertiary, a few 

 species also occur; and two or three living species are known. Two of the 

 latter are fount! in northern seas, and one is said to occur on the coast of 

 Japan. From the associates of some of the fossil species, they would appear 

 to have lived in warm climates. 



Amauropsis paliidiiisefoi-inis, H. & M. (sp.). 



Plate 19, figs. 15, a, b, c. 



Natica paludinaformis, Hall anil Meek (1854), Mem. Am. Acad. Arts ami Soi. Boston, V (new ser.), 389, 

 pi. iii, fig. 3 (not N. paludiniformis, d'Orbigny, 1850). * 



Amauropsis paludinceformis, Meek and Hayden (1860), Proceed. Acad. Nat. Sci. Philad., XII, 185. — Meek 

 (1864), Smithsonian Check-List N. Am. Cret. Fossils, 20. 



Shell subovate, rather thin; spire elevated and turreted; volutions 

 convex, last one moderately large and somewhat produced below; suture 



* I am not aware whether any one can tell to what genus Natica paludiniformis, d'Orbigny, belongs, 

 as I beleve no figure or full description of it has ever been published. In his Prodr. de Paleont., 

 II, 312, he merely says that it is near his Natica sinuosa, "but without a sinus in its coluuiellar lip; and 

 has its volutions slightly striated longitudinally." But all we know of his N. sinuosa is that he says, on 

 the same page of the same work, that "it is near N. spirata, but smaller, aud remarkable for having a 

 sinus of the columellar border near the umbilicus." Now his A r . spirata, he says, is Nerita spirata, Sowerby ; 

 ■which is a Carboniferous species, apparently of Naticopsis, McCoy. So it would certainly be a "pursuit 

 of knowledge under difficulties'' to undertake, from such a description, to determine even to what genus 

 his A", paludiniformis really belougs. If, however, it is congeneric with the Cretaceous shell here described, 

 and his species can be regarded as established, then it would be necessary to find another name for our 

 shell. 



