The number of true species is extremely doubtful, most of those 

 described being known by the imperfect original descriptions only. 

 A. virescens alone, is well known by VayssiSre's excellent work on 

 the Tectibranchs of the Gulf of Marseilles. 



The name Petalifera was proposed hy Gray as a subdivision under 

 Dolabrifera, in 1847 ; no diagnosis being given. Fischer proposed 

 Aplysiella for the same species in 1872, likewise without character- 

 ization of the group. 



Subdivisions. 



Petalifera s. sir. Shell squarish, with conspicuous posterior sinus ; 

 lateral teeth with long cusps. 



Pseudaplysia Pils. Shell oblong-ovate with the sinus obsolete; 

 lateral teeth with broad, blunt cusps. 



P. VIRESCENS Risso. PL 36, figs. 9, 10 ; pi. 55, figs. 10, 11, 12. 



Length 25 to 36 mill. Oval, narrower in front ; surface rough- 

 ened by low, tuberculous papillae, and sub-epidermal calcareous- 

 granules under the light spots. Mantle less developed than in 

 Tethys, consisting of a nearly hyaline membrane which covers only 

 the borders of the shell, most of the dorsal surface of which is ex- 

 posed through the large mantle-orifice. Pleuropodial lobes united 

 behind, with thick edges along the short dorsal slit ; foot broad and 

 fleshy. Gill milk-white. Genital pore situated a little back of the 

 anterior insertion of the pleuropodial lobes. Genital groove, anus, 

 etc. as in Aplysiidce generally. 



General color above reddish-brown, or greenish-brown with large 

 light spots ; lower surface pale grayish, with only traces of brown 

 spots, but with numerous whitish spots due to calcareous particles 

 sunken in the tissues. After death the body is a more or less strong 

 tint of greenish-yellow. 



Shell squarish, the beak projecting ; sinus deeply concave and! 

 wide. 



Nice (Risso, Robb & v. Beneden) ; Gulf of Marseilles (Vayssiere) ; 

 lives on floating fueus throughout the Mediterranean (Monts.). 



Aplysia virescente Risso, Hist. Nat. Eur. Merid., p. 42 ; A. vires- 

 cens t. c., p. 433, pi. 1, f. 10 (1826). Aplysia petalif era RANG, Hist. 

 Nat. Aplys., p. 52, pi. 5, f. 1-3 (1828). Aplysia unguifera RANG, 

 ibid., pi. 5, f. 4-7. Aplysiella petalifera and unguifera FISCHER, 

 9 



