THE NAUTILUS. 47 



more tlian in European forms, forming a conspicuously rimate um- 

 bilical region. Type E. novimundi. 



Pterides, n. gen. 



The shell is minute, rimate, long and narrow, composed of many 

 convex whorls, (7 to 10 in known species); apex obtuse, the first 

 whorl large. Aperture small, diagonal, elliptical, the peristome 

 thin, continuous, expanded throughout or at the ends, where it is re- 

 tracted to form shallow spout-like sinuses. Operculum and soft parts 

 unknown. Type P. pterostoma. 



These remarkable little snails are without relatives among known 

 American genera. They may be compared only with a genus found 

 about forty years ago in the flood-debris of the rivers of southern 

 France and Spain, and described by Bourguignat under the generic 

 name Paladilhia,^ and with another group, Laktktia^ described 

 from quaternary fossils found around Paris, but now known to inhabit 

 subterranean waters and springs of central Europe, where most of the 

 German species have been described as Vitrella Clessin. 



Both Pahidilhia and Lartetia are small, slender shells with the 

 aperture ovate, the outer lip bending forward below, retracted near 

 the upper insertion. In Paladilhia there is a rather narrow, Pleuro- 

 tomoid notch above, leaving a sort of indistinct sinus-band; in 

 Lartetia there is only a broad, rounded sinus. In my opinion the 

 two groups are not generically distinct, Lartetia being at most a 

 subgenus ol Paladilhia.^ 



These forms, and especially the Lartetia, are apparently the 

 nearest allies of the Mexican Pterides, which differs from them 

 chiefly by the diagonal, oblong aperture with broadly expanding lip. 



^Paladilhia Bourguignat, Monographic du Genre Palad., 1865. The type, 

 P. pleurotorna Bgt., is a snail measuring 4x2 mm., found in the drift debris of 

 the Lez, a little river near Montpellier, dept. de I'H^rault, and believed to in- 

 habit subterranean watercourses. 



^Lartetia Bourguignat, Catalogue des Mollusques terrestres et fiuviatiles des 

 environs de Paris a I'^poque Quaternaire (in E. Belgrand : Le Seine — 1, Le 

 Bassin Parisien aux ages Ant^historiques), pp. 15, 17 (1869). Type L. bel- 

 grandi Bgt. 



* The normal forms of the genus are those called Lartetia, Paladilhia being 

 an extreme development in one or two species only ; but the latter name has 

 priority for the genus, having been described in 1865, while Lartetia dates 

 from 1869. 



