558 PLEUROBRANCHID^. 



P. MK.MBRANACKUS, MoiltagU. 



Large, ovate, flat, perfectly membranaceous ; a mere vestige of 

 a spiral apex. 



Plate CXIV. F. fig. 5, and (Animal) Plate X. X. fig. ;5. 



Lamellaria meml/raiiacea, Mont. Trans. Linn. Soc. (1811), vol. xi. p. 184, pi. 1'-^, 

 f. 3, 4.— Gray, Encyclnp. Metiopolitana, Moll. pi. 3, 

 f. 15. 



Bulla „ TuRT. Conch. Diction, p. 25. 



Pleurobranchus mcmJjranaceus, Fleming, Brit. Animals, p. "291. — TJrit. Marine 

 Conch, p. 133, f. 76.— Brown, Illust. Conch. 

 G. B. p. 62, pi. 2, f. 9. — SowERBY, Genera 

 Shells, Pleurobranchus. — Sowerby (Jan.), 

 Man. Conch, f. 232. — Reeve, Conch. Syst. 

 vol. ii. pi. 154. 



Although the shield offers but few characters for de- 

 scription, no one who has ever looked upon a specimen 

 will subsequently fail to recognise it. It is extremely thin, 

 being indeed almost wholly membranaceous ; and is much 

 spread and very depressed, being merely convex. The 

 surface of the shell, which is more or less strongly tinged 

 with flesh -colour, is very shining, and has a subnacreous 

 lustre that at times passes into the metallic ; it is some- 

 what roughened by elevated wrinkles of increase. The 

 shape in the adult examples is nearly ovate, being nar- 

 rowed, but not peaked above, and broadly, yet bluntly, 

 rounded below. A mere vestige of a spiral apex is just 

 perceptible, and the situation of this rudimentary spire is 

 less lateral than in plumula. The entire internal area is 

 visible, as the curl or bending over of the body is very 

 trifling, and is confined to the extreme posterior portion of 

 the aperture : the pillar lip is simple and not reflected. 

 An average-sized individual that measured nineteen lines 

 long, was thirteen lines in breadth. When young the 



