PLETJROBRANCHUS. 11 



SHELL ear-shaped, membranous, semitransparent, glossy and 

 iridescent ; it is composed (as in Aplysid) of two layers, the 

 outer being skin-like, and the inner semicalcareous and sepa- 

 rable : sculpture, numerous fine concentric or transverse plaits 

 or folds, and microscopic scratch-like lines in every direc- 

 tion ; there are also a few irregular longitudinal wrinkles, 

 caused by an unequal contraction of the shell in drying : colour 

 pale reddish-brown or tawny : spire extremely small and ob- 

 scure, placed on the lower side near the narrower end ; it is 

 composed of two whorls, and coated over with a shelly enamel 

 in large specimens : mouth occupying nearly the whole of the 

 lower surface ; dorsal margin rounded and somewhat thickened ; 

 inner margin almost straight ; outer or ventral margin dilated. 

 L. 2. B. 1-25. 



HABITAT : Coralline zone, on the Devon coast (Mon- 

 tagu and others); Falmouth and Helford (Hockin); 

 Cork Harbour (Humphreys); Arran and Birterbuy, co. 

 Galway (Barlee) . It seems to be equally local beyond 

 our seas. I am not aware of any extra- British habitat 

 except the north of France (Daniel,, Reynaud, and Tasle), 

 Naples (Costa) , and Trieste (Stossich). Specimens from 

 the last mentioned place are much smaller than ours. 

 It may, however, be the P. testudinarius of Cantraine, 

 P. mamillatus of Schultz, as well as P. Forskalii and 

 P. tuberculatus of Delle Chiaje, although the shell is 

 described by Philippi as " minima." Possibly the spiral 

 portion only was extracted from the animal. Leach 

 named our species Oscanius argentatus. 



2. P. PLU'MULA*, Montagu. 



Sulla plumula, Mont. Test. Br. (i.) p. 214, t. 15. f. 9, and rign. 2. f. 5. 

 P. plumula, R & H. iii. p. 559, pi. cxiv. F. f. 6, 7, and (animal) pi. XX. 

 f. 1, 2. 



BODY semioval, gelatinous, lemoncolour, or whitish with a 

 slight tinge of yellow, marked with flake-white spots, minutely 



* A little feather ; from the gill-plume. 



