PART II. PLEUROBRANCHlNjE. 



361 



lobes ; shell none ; branchia naked, placed on the 

 right side of the body. 



G. Meckelii. Blainv. Man. de Malacol. pi. 45. f. 3. 



SUB-FAM. 5. PLEUROBRANCHIN^. 



Animal cheloniform, branchia pectinated, placed on 



the right side under the edge of the mantle which 



sometimes covers a calcareous shell. 



Umbrella Lam. Animal large and circular ; anus tu- 

 bular, placed behind the branchia ; tentacula two, 

 short, as in the next genus ; with eyes at the in- 

 ternal base, between which is a proboscis. Shell 

 resembling a limpet ; but the middle is thickest, and 

 the edges very sharp. 



U. Indica. Blainv. Man. pi. 44. f. 1. 



PLEUROBRANCHUS Cuv. Animal cheloniform ; body 

 overlapped by the mantle and the foot; the. former 

 sometimes contains a small oval plate, either horny 

 or calcareous ; mouth small, probosciform ; ten- 

 tacula two, tubular, and short, 

 citrinus. RUpp. Atl. i. 5. f. 1. Forskalii. Ib. pi 5. f. 2. 



PLEUROBRANCH^/A Meckel. Anus above the bran- 

 chia ; tentacula four, short, remote ; shell none ; 

 branchia and genital orifices as in the last. 

 Meckelii. Leve. Dissert. Griff. Cuv. xii. 43. 



ORDER DITHYRA. Bivalve Shells. 



TRIBE 1. TUBULIBRANCHIA Cuv. 



Animal inhabiting a tubular shell affixed to other sub- 

 stances and somewhat spiral at its tip ; tail turned un- 

 der the body and terminated by a thin operculum j 

 head obtuse, with two short tentacula with sessile eyes ; 

 mouth a vertical orifice with two filaments beneath be- 

 longing to the foot ; hermaphrodite.* 



* The animal of Magilis being unknown, I am afraid of including it in 

 this group. 



