128 PETALIFERA. 
Genus IV. PETALIFERA Gray, 1847. 
Petalifera Gray, A List of the Genera of Recent Mollusca, their 
synonyma and types, in P. Z. S., 1847, p. 162, type Aplysia petali- 
fera.—Aplysiella Fiscuer, Journ. de Conchyl., 1872, p. 296 (for A. 
petalifera and unguifera).— V AYssIERE, Rech. Zool. et Anat. sur les. 
Moll. Opistobr. du Golfe de Marseille, 1re Partie, Tectibranches, 
p. 71 (Ann. du Mus. d’Hist. Nat. de Marseille, Zool., ii). 1885. 
Body long-ovate, moderately convex, with the neck and head 
short and ill-defined ; eyes, anterior tentacles and rhinophores of the 
form usual in APLysIID#, the latter nearer to the anterior end than 
to the dorsal slit. Mouth with more or less developed lateral palpi. 
Pleuropodial lobes arising at or behind the middle of the length, 
contiguous, the right often overlapping the left, united behind, leay- 
ing a short gill-slit more or less open at the two ends; mantle thin, 
with a very large median orifice exposing the shell. Genital orifice 
within the slit, in front of mantle. Anus, genital groove, etc., as 
usual. Integument more or less warty in life. Foot very broad. 
Shell thin, hyaline, slightly concave and squarish, the posterior 
sinus wide and concave. 
Radula with the rhachidian tooth 5-denticulate, inner laterals 
with the cusp long, armed with 3 or 4 denticles on its outer edge; 
on the outer laterals these denticles increase in length, equalling or 
surpassing the main cusp (pl. 55, fig. 12, rhachidian, 1st and another 
lateral, 25th and 48d laterals). 
Distribution: Mediterranean, Japan. 
This genus differs from Tethys in the shortening and _ posterior 
union of the pleuropodial lobes, which no longer have the function 
of swimming organs ; in the less covered shell, more anterior genital 
pore, and in the teeth, the cusps of which lack the fine serration seen 
in Tethys, and have no denticles on the inner sides of the laterals. 
The section Aplysia of the genus Tethys, represented by T. 
punctata, depilans, etc., is somewhat allied to Petalifera in having a 
rather large mantle-orifice exposing the shell, and more or less broad 
union ofthe pleuropodia behind; but it differs widely in dentition, 
in the degree of development of the swimming-lobes and in numer- 
ous other features. Petalifera differs from Dolabrifera in the pres- 
ence of a large orifice in the mantle exposing part of the shell. 
The species live on Zostera and Algee, to the fronds of which they 
strongly adhere by the broad sole. Locomotion is wholly by creep- 
ing. 
