322 PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 



The radula is very slender; the outlines of the median plates are in- 

 distinct; they bear three very small, but distinct and nearly equal, den- 

 ticles; the lateral teeth have only two denticles. 



Length, 11™™; breadth, 5™'"; length of body-whorl, 7.10"'™; length of 

 aperture, 5™™ ; its breadth, 2.15™'". 



Off Martha's Vineyard, in 312 to 506 fathoms (stations 937, 917, 994, 

 997, 1029), 1881, fourteen specimens. 



This delicate species is liable to be confounded with the young of S. 

 pygina'us, but it differs decidedly in its dentition, operculum, nuclear 

 Avhorls, short and straight canal, and in the character of its spiral cin- 

 guli. The upper whorls of S. pyymtcus are much more angular, with 

 coarser and more prominent carinse or cinguli, which are separated by 

 narrower incised grooves.* 



This species, by its regular spiral nucleus, would be referable to the 

 gToup Siphonorhis. It also approaches Molinia Friele, by the characters 

 of its dentition and operculum. 



Troplion clathralus (Linn^j Holler. 



Off Chatham, Mass. ; stations 972, 976. in 16 fathoms. 



Astyris diaphana Verrill. 



Jstyris rosacea Verrill, Proc. Nat. Miis., iii,p. 408 {non Gould). 



Astyria diaphana Verrill, Trans. Conn. Acad., v, p. 513, j)l. 58, fig. 2, June, 1881. 



Shell thin, delicate, translucent, white, nearly smooth, elongated, 

 with a long, tapering, acute spire. Whorls eight, broadly and evenly 

 rounded ; suture somewhat impressed, but not deep, frequently narrowly 

 channelled. Surface, except anteriorly and on the canal, destitute of 

 spiral lines, unless microscopic striations, and of any indication of ribs, 

 but covered with very close, almost microscopic lines of growth, which 

 give the surface a dull appearance, when dry; on the canal and extend- 

 ing to the anterior part of the body-whorl are a number of distinct 

 spiral lines, becoming faint opposite the middle of the aperture. The 

 nucleus is larger than in A. romcea, rounded, depressed, and spiral, but 

 somewhat mammillary. The aperture is small, oblong-ovate; the outer 

 lip is sharp at the edge, but in adult shells has a. distinct thickening a 

 little back from the margin ; the inner surface is usually smooth, but in a 

 few adult examples it has a row of four or five small, transversely oblong 



* There are two varieties of «S'. ( Siphonorbis) pyijmwus on our coast, which are often 

 ■well-marked. The larger, typical form, from north of Cape Cod, has well-rounded 

 ■whorls, covered with strong cinguli and sulci, and with a strongly ciliated epidermis ; 

 canal long and much curved. The other variety, which abounds off" Martha's Vine- 

 yard, etc., in from 20 to 300 fathoms, on muddy bottoms, has the whorls flattened and 

 much smoother, the cinguli often obsolete, in part, except on the upper whorls, and 

 the epidermis dark green or olive, and only slightly ciliated, or often nearly or quite 

 smooth ; and the canal is perhaps a little shorter and less curved. This may take the 

 variety name, S. pygmcem, var. planulns. The nucleus and ajjical whorls agree well, 

 however, in the two forms. The generic names, Neptunella and Siphonella, formerly 

 used by me for this shell, are both preoccupied. 



