262 ATYS. 



The anatomy of the typical forms is unknown. In the section 

 AUeula, the frontal disc is wide-ovate, with no anterior or poste- 

 rior auricles; epipodial lobes developed much as in Scaphander, but 

 more prolonged posteriorly (pi. 59, fig. 16, 17, A. cylindrica, after 

 Ehrenberg). Eyes absent. 



In the subgenus Roxania, the large frontal disc is produced 

 behind in two triangular lobes, the epipodial lobes being as in 

 Alicula (pi. 59, figs. 13, A. utriculus}. Eyes absent; foot quadrate, 

 slightly bilobed behind. Gizzard-plates wanting. 



Dentition (of A. utriculus) with the formula 1*1*1 ; central teeth 

 well developed, with multicuspid cusp, slightly emarginate in the 

 middle. Laterals large, subtriangular, with no dentate cusps ; un- 

 cini wanting. It, therefore, agrees with Diaphana or Cylichna in 

 the form of the centrals, with Diaphana and Scaphander in the 

 absence of uncini; but it differs widely from all of these genera in 

 the form of the lateral teeth (see pi. 61, fig. 32, A. utriculus, after 

 Sars). 



The shell in this genus frequently resembles that of Cylichna or 

 of Scaphander, and the exact limits of these groups have not yet 

 been clearly indicated. It is likely that Atys should be restricted to 

 those forms in which the upper lip has an angular fold above its 

 insertion in the vertex, and the forms lacking this feature may then 

 be removed to constitute one or two distinct genera. We prefer to 

 leave the genus, for the present, in its old limits, believing that this 

 is preferable to a re-assortment of its contents prior to the necessary 

 examination of the soft parts in the various subgenera proposed. No 

 really intelligent systematic work can be done in this group by the 

 shells alone. 



The subgenera referred provisionally to Atys are as follows: 



ATYS s. sir. Shell swollen, having the lip plicate above the ver- 

 tex, the columella obliquely truncated or angularly folded. Type 

 A. naucum. 



ALICULA Ehrenberg, 1831. Shell cylindrical ; lip plicate above 

 the vertex ; columella not distinctly truncated or folded. Type A. 

 cylindrica. 



ROXANIA Leach. Shell cylindric-elliptical, with spiral punctured 

 stria? ; lip not twisted at its superior insertion ; columella subvertical, 

 slightly sinuous. Type A. utriculus. 



