26 



Pelseneer ') regarded conica as a transitional form between virgtila and acicula. The 

 dlfferences among his three species are mentioned here summarily: 



I. Shell. A. Initial portion of a dark brown colour. 



a. Shell itself with very marked dorsal curve-, transverse 



diameter rapidly increasing Clio virgiila. 



' b. Shell slightly curved ; the transverse diameter increases 



gently and uniformly Clio conica. 



B. Posterior extremity whitish. 



Shell long, slender, straight Clio acicula. 



II. Animal. A. Oesophagus very long; for that reason stomach and liver 



situated much behind Clio virgtila. 



B. Oesophagus short. 



a. Liver distinct Clio conica. 



b. Liver much reduced Clio acicula. 



I. As to the shell, I have seen a very great number of forms, and I agree with Boas, that 

 the limits between virgula and acicula are scarcely visible. The torms corniforniis, virgula., 

 conica., clava, acicula merge into one another. Besides, many specimens of acicula have a 

 brown-coloured embryonic .shell. 

 II. I did not find the oesophagus in conica and in acicula short, neither can I attach any 

 great importance to the liver, which is present, even in the very long a«V?//i3:-specimens. I 

 think that the anatomical differences vary gradually with the curvature of the shell. 



The difference between clava and acicula^ though slight, is somewhat greater than 

 between the other forms. Though clava was referred by Souleyet, by Boas and by Pelseneer 

 to acicula, I believe it belongs to virgula. 



Therefore I have referred all the forms with a curved shell (corniformis., virgula, conica) 

 to the species virgula. Also the very short straight form clava. 



On the other hand I have referred the specimens with very long, slender, straight shells to 

 the species acicula. Styliola vitrca was referred by Boas to Crcseis virgula, by Pelseneer to Creseis 

 conica. The figure of Verrill shows the fins rounded, but this is most probably a mistake. 



The e.vtremity of the shell in virgula and acicula shows two very slight constrictions, 

 the anterior of which, tolerably distinct in the first species, gradually disappears in acicula 

 (See Boas, Spol. atl. figs. 40 — 33). 



Subgenus Hyalocylix Fol. 



1828. Creseis {part.} Rang, Notice sur quelques Mollusques nouveaux etc, Ann. d. Sc. Nat., 



sér. I, vol. XIII, p. 302. 

 1875. Hyalocylix Fol, Sur Ie dcveloppement des Ptéropodes, Arch. d. Zool. Exp., sér. i, 



vol. IV, p. \j-j. 

 1875. Styliola {part.) Auctorum. 

 1875. Cleodora {part.} Auctorum. 



i) ChalL Kep. LXV, p. 50. 



