HOMALOGYRA. 69 



species of Rissoa. In the ' Microdoride Mediterranea ' 

 of Costa (1861) the present genus is described under the 

 name of Ammonicerina. 



31 1. HOMALOGYRA A'TOMUS *,(Philippi.) M*l 



Truncated a atomus, Phil, in Arch. f. Nat. (1841) vii. pt. 1. p. 54, t. v. 

 f. 4. Skenea nitidissima, F. & H. iii. p. 158, pi. kxiii. f. 7, 8. 



BODY yellowish-white on the upper side, and of a paler hue 

 underneath, nearly hyaline : snout or head- veil short, broad, 

 expansile and very flexible, forming in front two semicircular 

 lobes ; these lobes are sometimes separated by an intermediate 

 membrane, which slightly projects, so as to make the extremity 

 appear trilobed ; the front part is usually, but not always, 

 clothed with numerous irregularly disposed cilia of different 

 lengths and sizes ; when fully extended this part is so trans- 

 parent that the foot can be seen through it : tentacles none, nor 

 the slightest vestige of any, in whatever position or light the 

 animal is viewed : eyes large in proportion, seated about half- 

 way between the front edge of the shell and the extremity of 

 the snout: foot lanceolate, slightly bilobed in front, and 

 rounded or bluntly pointed behind : opercular lobe sometimes 

 having on its upper margin a few cilia like those on the snout. 



SHELL resembling in shape a miniature Planorbis corners, 

 not very thin, semitransparent, and glossy : sculpture, usually 

 fine and close-set indistinct striae in the line of growth, but occa- 

 sionally also some obscure ridges in the same direction on the 

 first-formed whorls, and a few white varicose streaks on the 

 body- whorl : colour reddish-brown or pale tawny : spire sunk 

 below the level of the last whorl ; apex blunt : whorls 3, com- 

 pactly coiled, rounded on the upper side, and somewhat angu- 

 lated or flattened on the under side ; the last nearly enwraps 

 all the rest, which are exceedingly small : suture deep : mouth 

 projecting a little outwards, with a sharp and even edge; it is 

 indented behind by the periphery : umbilicus wide, open, and 

 almost flat, fully exposing the interior of the spire : operculum 

 clear- white, flat, with 3 or 4 gradually increasing turns, which 

 are defined by a thickened edge, and obliquely but slightly 

 striated. L. 0-0125. B. 0-035. 



Yar. vitrea. Shell of a glassy transparency. 

 * An atom. 



