68 ARCADE. 



little depth, with a sand-like rusty-brown belt, and a darker 

 interrupted line nearer the margin, which is finely dentated ; 

 but there are no equidistant points or ocelli, as in the last 

 species. The mantle is without siphonal folds. The foot is 

 white with a deep fissure at the bend, and is provided with a 

 green filamentous membrane for attachment, which has all the 

 same incidents as in Area tetragona. The foot is pure white, 

 and can be exserted to a considerable length; it is fleshy, 

 tapers cylindrically, and is very like that of Galeomma. 

 There are on each side a pair of similar-sized, very thin, pale 

 yellow symmetrical branchiae, which gradually taper and unite 

 around the mouth, forming a double lamina, of the same 

 character as in Area tetragona and Pectunculus glycimeris. 



This species is frequently taken free in the dredge, in the 

 coralline zone at Exmouth, and also fixed by the byssus 

 amongst the masses of Serpula in old bivalves. 



We had in our possession the identical Area barbata first 

 introduced as British by Dr. Turton in his ' Conchylia Di- 

 thyra/ and, on showing it to Dr. Goodall, he expressed an 

 opinion that it was an exotic specimen. 



We have not seen alive the 



A. RARIDENTATA, Searles Wood. 

 A. raridentata, Brit. Moll. ii. p. 241, pi. 45. f. 8. 



PECTUNCULUS, Lamarck. 

 P. GLYCIMERIS, Linnaeus et Auct. 



P. glycimeris, Brit. Moll. ii. p. 245, pi. 46. f. 4, 5, 6, 7 ; and (animal) 

 pi. P. f. 6. 



Animal suborbicular, lentiform, bluish white ; mantle open 

 throughout the periphery of the shell, except the dorsal line ; 

 the margin is plain, having its upper surface for the depth of 

 an eighth of an inch powdered with minute sand-like, pale 

 red, brown or black points. There are at the posterior side, 

 for half its length, at the verge of the mantle, about twenty- 

 five minute equidistant black dots or ocelli, besides short, 

 brown, transverse bars; the under surface is marked with 

 short flake-white cross-lines. The mantle has neither tubes nor 



