NO. 1139. i>Ei-:r-\v. \rr.u MOLL i sc.t rr-:i;i;iu. .txi> r.rsn. 879 



. 



nearly straight, the less oblique and considerably the longer, and forms 

 a broad angle with the anterior. There are in the largest examples 

 about eleven or twelve teeth in the anterior series, counting four or 

 five very small proximal ones; and in the posterior series, fifteen or 

 sixteen teeth of which the five or six proximal ones are minute. In 

 ninny specimens the two series are not distinctly separated under the 

 beak, in others there is a very minute, edentulous space in line with 

 the minute ligamental notch. The largest teeth in the middle of each 

 series are very elongated, erect, acute, with the tips turned upward 

 toward the margin. The surface of the shell is covered with very 

 regular, concentric sulcations separated by narrow, evenly rounded 

 ridges of about the same width; in most cases this sculpture is 

 faint or nearly obsolete toward the postero-dorsal margin and on the 

 umbos. In many specimens, a number of faint radiating stria- run 

 from the umbos to the antero-ventral margin, similar lines sometimes 

 occur posteriorly. The epidermis is without much luster, of either 

 greenish yellow, light yellow, or straw color, more or less iridescent, 

 especially near the umbos. Along the dorsal margin the outline of 

 the teeth can be imperfectly seen through the substance of the shell. 

 The interior in fresh specimens is lustrous bluish white and in some 

 cases is distinctly tinged with pale flesh-color. The muscular and pal- 

 lial impressions are usually indistinct but some specimens show a small, 

 but distinct, angular pallial sinus. 



The alcoholic specimens when dissected were found to have a short 

 siphon and a large, stout foot with a broad disk having strongly creii- 

 ulated edges. The labial palpi were long, crescent-shaped and the 

 tentacle-like appendages arising from the outer bases of the external 

 palpi were very long, slender, and coiled in a spiral. The gills were 

 long, narrow, and prismatic, one on each side. 



Length of one of the largest specimens, (3.5 mm.; height, 4.6 mm.; 

 thickness, about 3.5 mm. 



Young specimens about 2 mm. long are more equilateral than the 

 adults and have the posterior end less produced and more evenly 

 rounded, the umbos decidedly prominent, and the surface covered with 

 fine, regular, concentric .grooves, the epidermis showing distinct iri- 

 descence. 



Found in large numbers, at many stations, between X. lat. 42 47'. W. 

 long. 61 4', and K. lat. 35 9' 50", W. long. 74 57' 40", in 125i to 1,731 

 fathoms, 1883-1887. 



This species shows considerable variation in form when a large series 

 of specimens from the same locality are compared. Some are decidedly 

 more elongated and tapered posteriorly than the typical form, others 

 are somewhat shorter and more regularly ovate with the posterior end 

 blunter or more rounded; all agree essentially in sculpture and in the 

 peculiar structure of the hinge and ligament. 



This species has some resemblance to N. sericca Jeffreys, of which it 



