366 pleurobranchid^. 



Family PLEUROBRANCHID^. 



Shell limpet-like or concealed, rarely wanting ; mantle or 

 shell covering the back of the animal ; gill lateral, between the 

 mantle-margin and foot ; food vegetable, stomach extremely 

 complicated. 



The animals of this family have no upper jaw, the lingual 

 membrane is armed with numerous short teeth, arranged in a 

 quincunx ; there are four stomachs, the second of which is fleshy, 

 and sometimes furnished with bony pieces, and the third is pro- 

 vided internall}" with prominent longitudinal lamellae; the 

 intestinal canal is short. The species are tolerably numerous, 

 occasionally of large size and adorned with varied colors ; the}' 

 are mostly inhabitants of the high seas. 



Pleurobranchus, Cuvier. 



Etym. — Pleu7-a, side, branchia, giW. 



Syn. — Berthella, Bl. Oscanius, Gray. Haliotinella, Souverb. 



DiHtr. — 22 sp. South America, Norway, Britain, Mediteria- 

 nean. Red Sea, Ceylon. P. citrinus, Riippell (Ixxxix, 82, 83). 



Shell internal, large, oblong, flexible, slightly convex, lamellar, 

 with a posterior, subspiral nucleus. 



Animal oblong, convex ; mantle covering the back and sides, 

 papillated, containing spicula ; foot large, separated from the 

 mantle by a groove ; gill single, free at the end, placed on the 

 right side between the mantle and foot ; orifices near the base 

 of the gill; head with two grooved tentacles, eyes at their outer 

 bases ; mouth armed with horny jaws and covered by a broad 

 veil with tentacular lobes. 



PLEUROBRANCH^A, Meckel. (Pleurobranchidium, Blainv.) 

 Mantle-margin very narrow, not concealing the gill; dorsal 

 tentacles ear-like, oral veil tentaculiform. P. Meckelii, Blainv. 

 (Ixxxix, 90). 



KOONSiA, Verrill, 1882. (Dedicated to B. F. Koons, U. S. Fish 

 Commission.) Allied to Pleurobranchsea, with which it agrees 

 in the character of the head, tentacles, proboscis and gill. It 

 differs in having the back swollen and overhanging both on the 

 sides and posteriorly, and a distinct mantle-edge all around, 

 with a wide groove between it and the foot posteriorly, as well 

 as laterally ; the foot is narroM^er and prolonged posteriorly, 

 with a specialized glandular area, near the end, beneath, and a 

 conical papilla above near the tip. The external reproductive 

 organs appear less complicated than in Pleurobranchaea. The 

 verge is armed with small hooks, but the spicule, present in the 

 latter genus, is not protruded, if present, in the specimens of 

 Koonsia ; urinal opening at the anterior root of the gill ; between 

 this and the verge, some specimens show a small opening and a 

 low papilla, but none show the large opening and long flat papilla 



