MUSEUM OF COMPARATIVE ZOOLOGY. 385 



The armature of the mouth is a character which does not appear until full ma- 

 turity, so that I do not rcf^mrd its non-existence in the ChaUenger specimens as 

 important. The other cliaracters seem to agree closely with Watson's figure 

 and description, and, taking into consideration the known variability of the 

 abyssal shells and among thb Blake specimens of this species, I do not feel jus- 

 tified in separating the JUake shells specihcally from D. costulata. If I am 

 correct in the identitication, this material enables me to add a good deal to the 

 knowledge of the species and genus. The dried remains of the animal in one 

 specimen bear a pellucid multispiral operculum a little more circular in outline 

 than that of Seguenzia, but otherwise precisely like it. 



The aperture in the adult is strongly thickened a little distance within its 

 margin, which remains sharp. The projecting peripheral part is a little bent in, 

 recalling the aperture of Seguenzia. The callus on the body is thin and 

 smooth, that within the outer lip is broad, thick, iridescent, and deeyjly grooved 

 parallel with the external spirals, producing four or five ridges between the 

 grooves above the carina and a larger number of rather smaller ones below it. 

 The columella is thickened concave and strongly reflected, its basal extreme 

 terminating in a stout tooth-like twist of the margin, beyond which is a deep 

 sulcus in the callus extending nearly across the base, in the middle of which rises 

 a solitary stout tooth-like ridge. The walls of the umbilicus are nearly smooth, 

 and as regards the individual turns are somewhat concave. The nucleus in this 

 form gives the impression, after very close scrutiny of several fresh specimens, 

 that it is really laid at right angles to the original axis and half immersed in 

 the first post-nuclear turn. This is masked by the fact that the nucleus proper 

 occupies less than a single turn, and appears thus more normal than it really is, 

 if my suspicions are correct. 



Solarium reticulaium Philippi is referred to this genus by Watson, and is 

 said to have been dredged by the Porcupine at various stations in the North 

 Atlantic. 



Family DELPHINULID^. 



Genus LIOTIA Gray. 



Liotia Gray, Syn. Brit. Mus., 1840 (no description, type Delphinula cancellata Gray); 

 P. Z. S. 1847, p. 145. 



This group was separated from Delphinula Lamarck (Angaria H. & A. Ad- 

 ams) to comprise the small species with a thickened margin to the aperture 

 and less brilliant nacre than the large forms. Gray's type was a cancellated 

 species, and the genus Liotia, in the most restricted sense, Avill comprise those 

 species which have numerous varices or radiating circumambient ribs cancel- 

 lated more or less by spiral sculpture. 



Those species having a single varix marking the finally adult condition, 

 generally with strong spiral ridges on the periphery, which may or may not 



VOL. xviii. 25 



