102 



interior polished, porcellanous, simple or chambered by a dia- 

 phragm or variously shaped process, supporting the viscera; 

 peristome entire. No operculum or attached base. 



Subfamily Hipponycinas. 



Animal without foot, properly so-called ; adductor muscle 

 fixed to the interior of the shell above, and below either to the 

 substratum excavated in the surface of the body on which the 

 mollusk is attached, or to a ventral calcareous opercular-like 

 piece which completely closes the aperture ; inferior surface of 

 the body encircled by a sort of ventral mantle with papillary 

 margins, resembling the dorsal mantle and morphologically cor- 

 responding to the epipodium ; muzzle long, deeply incised and 

 terminated by two lateral lobes ; tentacles long, subulate, the 

 eyes sessile towards their base ; a spatuliform growth below the 

 neck ; radula as in Calyptrseinse, the marginal teeth denticulated. 



Shell conical, peristome simple, with or without an internal 

 process attached at the apex, but an opercular piece normally 

 forms the base to the shell and is soldered to the surface of the 

 body on which it lives attached. The embryonic Hipponyx has 

 a spiral shell. 



These gastropods have so aberrant an appearance that they 

 have been classed as Rudistes (Sowerby), and Brachiopoda 

 (Morris), the opercular piece being taken for a ventral valve. 



Synopsis of Genera. 



I. CALYPTR^EINJE. 



Genus CRUCIBULUM, Schum., 1817. 



Differs from Calyptraea (described below), in having an in- 

 ternal cup-shaped lamina, the margin, of which is entire, and 

 which is attached on one side to the inner wall of the shell. 

 Temperate and tropical seas. 



Dentition, PI. 30, fig. 2. 



The synonyms are Trelania, Catillina, and Neleta, Graj', 

 1867 ; Dispotsea, Say, 1826, and Calypeopsis, Lesson, 1830. 



Section BICATILLUS, Swainson, 1840. 



Cup open and reduced to a curved lamina, adhering for its 

 entire length. Indian Ocean. Fossil in the miocene of Aqui- 



