MUSEUM OF COMPARATIVE ZOOLOGY. 55 



a half nuclear whorls yellow-brown, beautifully reticulated with wavy transverse 

 lines, then changing suddenly into waxy white ; remainder of shell with spiral 

 threads, set in pairs which frequently blend to make one flattened spiral thread, 

 with wider interspaces between the threads. Two or three threads next the su- 

 ture are stronger and wider apart than the others, the outer one strongest, giving 

 the whorl a turreted appearance, and rising into little knobs on the transverse 

 ridges; these ridges rather sharp, sixteen to eighteen in number, fading away 

 toward the canal in most but not all specimens, flexuous with the lines of 

 growth ; pillar straight, the edge obliquely cut off, shorter than the aperture 

 anteriorly ; a light deposit of callus on the body ; aperture proportionally 

 wide, thin-lipped, about half as long as the shell. Lon. 8.25. Lat. 5.25 mm. 

 Den. very variable. 



Off Cape San Antonio, 640 fms. Yucatan Strait, 640 fms. 



Var. extensa. 



Shell in most features like the last, but more elongated, with nine whorls, the 

 revolving threads (except the sutural ones) obsolete except near the anterior 

 end of the last whorl ; with a tendency of the thread next the suture to be 

 stronger and more strongly knobbed than (as in the normal form) the outer 

 one ; the transverse threads twenty to twenty-five, more numerous and in 

 large specimens hardly noticeable except near the suture ; spire nearly equal 

 to the last whorl and aperture about one third of the shell. Lon. 12.5. Lat. 

 5.0 mm. 



Off Cape San Antonio, 640 fms., 413 fms. Station 35, Lat. 23° 52', Lon. 

 88° 58' W., 804 fms. 



The sutural knobbing characterizes so many abyssal shells that it would 

 seem to have some significance, but what it is we are not yet able to determine. 



P. (Bela) limacina n. s. 



Shell waxy white, smooth, glistening, elongated, rather acute at both extrem- 

 ities ; whorls eight or nine, the nucleus and nuclear ones as in the last except 

 that they are less strongly sculptured ; next the suture, which is by them dis- 

 tinctly marked, a succession of (on the last whorl sixteen) little squarish knobs, 

 not continued anteriorly in any way, but looking as if they had been pinched 

 up from the interspaces between them ; on the back of the canal are two or 

 three spiral threads, remainder of shell without trace of spiral BCulptore : lines 

 of growth very flexuous, indicating a deep broad emargination near the suture ; 

 but the shell is so excessively thin and brittle that I can find, among many 

 specimens, none with a perfect aperture, but suppose from the growth lines 

 that the outer lip was rounded out broadly, while the canal is very narrow, the 

 pillar extremely thin, sharp and straight, making the aperture narrowly lunate. 

 There are variations in slenderness and in the prominence of the sutural knobs, 

 otherwise this is one of the most characteristic abyssal species and wholly un- 

 like any of the shallow-water Belas. Last whorl twenty-seven forty-fourths of 



