MUSEUM OF COMPARATIVE ZOOLOGY. 383 



strong spiral alternated ribs, one of the smaller just below tbe suture ; a large 

 spiral on the periphery and four on the base; crossed by numerous obliquely 

 radiating threads, which make the early whorls coarsely reticulate with nodules 

 at the intersections, while in the later whorls the radiations become less marked 

 and the spirals more numerous and more conspicuously nodulous. Whorls 

 rounded, apex a little blunt, suture distinct, not channelled, base rounded, um- 

 bilicus none; pillar nearly straight, with a strong tooth near its base, aperture 

 rounded, oblique, a little descending above, with six or eight stout lirse ending 

 in toothdike nodules, body with a moderate layer of nacreous callus. Alt. 5.0, 

 max. diam. 4.5 mm. 



Habitat. Off Havana, in 119-450 fms. Samana Bay, Santo Domingo. 

 Nassau, Bahamas. Various collections from the " West Indies." 



This little shell is proportionally more depressed, and has fewer spirals 

 when young, and owing to the persistent lirse looks adult at almost any stage. 

 It is extremely lovely when color and sculpture are perfect and fresh, but often 

 is wholly whitish. I have found it labelled by the name of punctiger A. 

 Adams, a much larger umbilicated species from the Indo-Pacific region. 



I have not been able to find a description of it, or any figure closely resem- 

 bling it. 



*b 



Genus BASILISSA Watson. 

 Basilissa Watson, Journ. Linn. Soc., XIV. p. 593, April, 1879. 



Shell trochiform, umbilicate, nacreous, sculptured. Pillar concave, its distal 

 end projecting as a strong tooth. Margin of the aperture concavely sinuate 

 near the suture and on the base. Peripheral margin produced, claw-like, be- 

 tween the two shallow sinuations. A grooved or denticulate callus in the 

 adult on the body whorl and within the margin of the aperture. Aperture 

 sub-rhomboidal. Operculum multispiral, horny, with a circular callus on the 

 inner central face and a subcircular outline. Example, B. costulata Watson. 



The above amended diagnosis is rendered necessary by the discovery of 

 adult specimens among the Blake shells. It is probable that most of the 

 species in an adult condition conform to it. It is conch ologically related to 

 the genus Seguenzia, a transition from which is indicated by such species as 

 S. carinata, S. elcgans, and S. trispinosa. But the soft parts as yet are un- 

 known. Should it be found, however, that some species do not exhibit the 

 denticulation, etc. described in B. costulata, and conform to the edentulous 

 type indicated in Watson's original description, (and B. alia may prove to be 

 of this character,) these would of course retain the original name of Basilissa, 

 while for the dentate forms the name of Ancistrobasis might be used. 



I have placed these species after the Tvochidaz in accordance with the general 

 custom, but I do not feel confident that the eventual position of all the species 

 will be here. 



