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 Linné’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., Régne Animal, ii, p. 398.—Bursatella BLAINy. 
(? Brit. Eneycl. Suppl.), Fér., Dict. Class. Hist. Nat., ii, p. 588 
(1822).—Aclesia Rane, Hist Nat Aplys., p. 68 (1828).—Stylo- 
cheilus Guip., 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 (pl. 40, f. 6), with well developed triangular rhachi- 
dian teeth with serrate cusp; the laterals narrower, with the cusp 
Jong and serrate on both edges (pl. 40, fig. 7). Marginals with 
the basal plates shorter, cusps longer (pl. 40, figs. 5,8). Jaws wide, 
composed of many minute chitinous elements (pl. 40, fig. 9). 
Type NV. 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 Aelesia. 
