A. E. Verrill — Mollusca of the New England Coast. 433 



trally ; in advance of this swollen part the shell narrows rapidly to 

 the aperture, the decrease being much the greatest on the dorsal side. 

 The aperture is oblique and elliptical in outline, the dorsal margin 

 being distinctly flattened. From the anterior swelling the shell 

 tapers regularly and gradually backward, with an increasing curva- 

 ture. The posterior opening is not very large, a little flattened, and 

 its margin, when perfect, has a moderately deep notch on each side 

 and a shallower one both above and below. The shell is translucent, 

 and the surface is everywhere smooth and polished, but shows irreg- 

 ular alternating bands of lighter and darker shade, due to greater or 

 less transparency of the substance, and there are also faint longitud- 

 inal whitish lines visible in the substance of the shell, but not affect- 

 ing the surface. 



Length, 22'"'° ; greatest diameter, 4'""' ; breadth of the oral aper- 

 ture, 2'"'" ; diameter of posterior aperture, 1'""'. 



Station 2,043, in 1,467 fathoms, 1883, (No. 38,116); stations 2,174, 

 2,221, 2,222, 2,228, in 1,525 to 1,594 fathoms, 1884. Taken in the 

 largest numbers at station 2,221, Avhere about twenty-five specimens 

 occurred, part of them living, (No. 40,498). 



This species is remarkable for its great size, exceeding even C. 

 grandis ; for its gibbous swelling close to the anterior end ; and for the 

 rapid and strongly marked contraction of the oral aperture. By the 

 last named feature it is readily distinguished from C. grandis. (See 

 plate xliv, fig. 17). 



LAMELLIBRANCHIATA. 

 Periploma undulata Verriii, sp. nov. 



Shell thin, translucent, rather small, compressed, long-ovate, with 

 the beaks a little prominent, situated somewhat in advance of the 

 middle. The anterior end is broadest, somewhat produced and 

 obtusely rounded, with a slight undulation running from the beak to 

 the anterior ventral margin, which is evenly convex in the middle, 

 but is so drawn in as to form a slight emargination at the commence- 

 ment of the posterior portion; a rather broad, shallow, but well- 

 defined groove runs from the beak to the basal emargination ; back 

 of this the posterior portion is rapidly narrowed to the rather small, 

 subtruncate tip ; a slightly elevated and roughened ridge runs from 

 the beak to the lower angle of the posterior end ; and several finer, 

 radiating lines cover the posterior surface above it. The anterior 

 dorsal margin is convex, and slopes very gradually ; the posterior 



