ART. 18 SMALL SHELLS DREDGED BY '' ALBATROSS ^ ' DALL 27 



layer of enamel over the body; interior smooth, except for a delicate 

 rib emerging from the spire and extending about half way to the 

 outer lip. Height, 3.5; breadth, 2; convexity, 1.2 mm. U. S. Nat. 

 Mus. Cat. No. 107933. 



Off Fernandina, one specimen. 



There is an ill-defined shallow constriction on the posterior part of 

 the whorl, but this may be pathological. 



Family TURRITIDAE 



The members of this family in the collection are numerous but all 

 small and white or translucent. Owing to the fact that their anatomy 

 is unknown and even the presence or absence of an operculum can not 

 be determined, the generic names used in this paper are merely ten- 

 tative. The nomenclature of the group is so unsettled and in nearly 

 all cases based merely on the shell characters, that no final arrange- 

 ment is at present possible. 



There have been several attempts at classification by nuclear 

 characters, and in some minor groups they may be useful. I have 

 elsewhere^ given my reasons for considering that the nucleus in 

 general has no fundamental generic importance, but that its characters 

 are adaptive, either to a swimming larval stage or one that is relatively 

 sedentary; with minor differences due to development in shallow or 

 deep water. There is no doubt that an abyssal habitat tends to 

 promote a smooth swollen or even mammillary protoconch and gyrate 

 pillar with a pervious axis. These characters are probably related 

 to the pressure of the deep sea environment. 



SPECIES WITH SWIMMING LARVAL STAGE AND SINUSIGEBA NUCLEUS 

 DAPHNELLA ? HYPERLISSA Dall 



Daphnella sofia, var. hyperlissa Dall, Bull. Mus. Comp. Zool., vol. 18, No. 29 

 pt. 2, 108, June, 1889. 



Two immature specimens off Fernandina. Also off Cape Fear, 

 North Carolina, at station 2678, in 731 fathoms, ooze, bottom tem- 

 perature 39.8° F.; United States Bureau of Fisheries. 



GYMNOBELA IMITATOR, new species 



Shell minute, white, with a Sinusigera nucleus of two and a half, 

 and nearly four subsequent whorls; suture distinct, appressed; whorls 

 only moderately convex; axial sculpture of (on the last whorl about 

 14) narrow, oblique ribs with wider interspaces, crossing the whorls, 

 stronger on the earlier whorls, and ending in small close beadlike 

 pustules in front of the suture; these ribs become obsolete on the base; 

 spiral sculpture of a single carina near the periphery of the whorls, 

 prominent where it intersects the ribs, and 10 or 12 fine threads in 



Proc. Washington Academy of Sciences, 1924, pp. 177-180. 



