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 FISCHER, Journ.de Conchyl., 1872, p. 296 (for A. 

 petalifera and unguifera). VAYSSIERE, Rech. Zool. et Anat. sur les 

 Moll. Opistobr. du Golfe de Marseille, Ire 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 APLYSIIDJE, 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, leav- 

 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 (pi. 55, fig. 12, rhachidian, 1st and another 

 lateral, 25th and 43d 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 of the 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 Algse, to the fronds of which they 

 strongly adhere by the broad sole. Locomotion is wholly by creep* 

 ing. 



