202 BULLETIN OF THE 



Pteronotus tristichus n. s. 



Plate XV. Fig. 3. 



Shell pure white, thin, polished, delicate, with six rather loosely coiled, 

 rounded whorls ; body more slender than in the last species, sutures much 

 deeper and not appressed. Nucleus large, loosely coiled, glassy, white ; varices 

 making about one quarter of a revolution around the spire, very thin, edges 

 dentate, prolonged on the shoulder of the whorls into a long pinna with a flat 

 central rib; below there are three other less prominent ribs, which project at the 

 edge of the varix on the last whorl; there is no transverse sculpture except 

 incremental lines, nor any inter- varical ribs; the spiral sculpture is obscure and 

 very faint, except the ribs on the varices ; aperture small, pear-shaped ; canal 

 open, rather long, bent to the right, the canal belonging to the preceding varix, 

 behind it, persistent and bent to the left. Max. Ion. of shell, 15.5; of last 

 whorl, 11.0; of aperture, 3.3; max. lat. of aperture, 2.0; of shell, 10.0 mm. 



Habitat. Station 51, off Havana, in 243-450 fms., Sigsbee. Station 5, 

 152-229 fms., off Cuba. 



This is a very elegant little shell, and not like any of the shallow- water 

 species. 



Genus EUPLEURA H. & A. Adams. 



This genus, separated from the Tritoniidw by Stimpson, with the type 

 Eupleura caudata Say, is a Pteronotus with irregular and more numerous 

 varices. It has been referred to Trophon as a subgenus by Kobelt, but, while 

 admitting that some of the Trophons are more nearly related to Eupleura than 

 to the type of Trophon, I think the dentate aperture and heavy primary varices, 

 the texture and habits of the shell, the station occupied by the animal on the 

 shores, and its subtropical preferences as to habitat, all point to a distinction 

 wortlry of preservation. I would, therefore, rather remove the muricoid Tro- 

 phons, or rather the muricoid species which have been included with the real 

 Trophons, to the vicinity of Eupleura, than sink the differences by a transfer in 

 the opposite direction. I should not retain among the typical Trophons any of 

 the species with a contracted callus and dentate aperture, or with varices' of 

 which part are distinguished from the others by a heavy deposit of shell 

 substance. 



Eupleura caudata Sat. 



Ranella caudata Say, Journ. Acad. Nat. Sci. Phila., II. p. 236, 1822. 

 Eupleura caudata Stimpson, Am. Journ. Conch., I. p. 58, pi. viii. fig. 5, 1865. 



The range of this species, as exhibited by the specimens of the National 

 Museum, extends from Cape Cod to Charlotte Harbor, Florida. The northern 

 specimens are rather larger, rougher, with the longitudinal sculpture more equal 



