NOTARCHUS. 135 



and distinct depression of the peripheral region of the body, to- 

 gether with the lack of a shell, seem to indicate that this little- 

 known form belongs to Fischer's genus Phyllaplysia. It has not 

 been noticed by authors subsequent to Rang. There is no conflict 

 between the name of this species and Linne's Tethys limacina ; the 

 latter was not referred to Aplysia until long after the date of de 

 Blainville's description. 



Genus VI. NOTARCHUS Cuvier, 1817. 



Notarchus Cuv., Regne Animal, ii, p. 398. Bursatella BLAINV. 

 (? Brit. Encycl. Suppl.), Fer., Diet. Class. Hist. Nat., ii, p. 588 

 (1822). Aclesia RANG, Hist Nat Aplys., p. 68 (1828). Stylo- 

 ckeilus GLD., U. S. Expl. Exped., p. 224 (1852). 



General form long ovate or fusiform, plump in the middle. Ten- 

 tacles, rhinophores, eyes and genital groove as usual in the family. 

 Pleuropodial lobes broadly united behind over a large gill-cavity, 

 their anterior ends contiguous, free margins short, contiguous ; the 

 dorsal slit subcentral and short. Mantle membranous, small, not 

 covering the long, arcuate gill. Genital pore near anterior end of 

 dorsal slit. Foot narrower than the body, long, acute behind. 



Shell very minute and orbicular, or wanting. 



Radula wide (pi. 40, f. 6), with well developed triangular rhachi- 

 dian teeth with serrate cusp ; the laterals narrower, with the cusp 

 long and serrate on both edges (pi. 40, fig. 7). Marginals with 

 the basal plates shorter, cusps longer (pi. 40, figs. 5, 8). Jaws wide, 

 composed of many minute chitinous elements (pi. 40, fig. 9). 



Type N. indicus Schweigger. 



This genus differs from Phyllaplysia in the plump, elevated body 

 and narrow sole ; from all other genera it differs in the minute or 

 obsolete shell. 



Subdivisions. 



No subdivisions of much value have yet been defined in this 

 genus. The following sections are generally recognized, but their 

 differential characters are unimportant. 



a. Plump ; sole a narrow band ; integument tuberculate or 

 smooth ; labial processes not developed (?) Notarchus. 



aa. Integument with filaments or fringed appendages; labial pro- 

 cesses developed 



b. Fusiform, the two ends attenuated, Stylocheilus. 



bb. Stouter, foot wider, labial processes broad Aclesia. 



