HELIX-STYLODONTA. 85 



In the peculiar thickening or duplication of the peristome this 

 species stands alone. It is the smallest of the Ceylonese Acavus. 



Section IV. STYLODONTA Cristofori & Jan. 



Stylodonta C. & J., Catal., p. 2, 1832 ; type, H. unidentata. 

 PFEIFFER (in part) Nomencl. Hel. Viv., p. 170, 1881. FISCHER 

 Manuel (as sect, of Acavus]. TRYOX, Manual of Couchology, 2d 

 Series, ii, p. 5, 26 (as sect, of Rotula, a subg. of Nanina). Stylodon 

 BECK, Index Moll., p. 46. ALBERS (in part) Die Heliceen, edit. 

 Martens, p. 149. Columplica HARTMANX, Gastropoden Fauna 

 Schweitz, p. 187 (as subg. of Helix). Pachya ALBERS (in part) 

 Die Heliceen, p. 107, 1850. 



The shell in Stylodonta is irnperforate, the axis a solid pillar, not 

 perforated even in the young. In contour it is globose-depressed, 

 wider than high, with conoidal blunt spire. The texture is strong and 

 solid, opaque ; the surface peculiarly sculptured. Color chestnut- 

 brown or yellowish ; whorls about 5, very gradually widening, some- 

 what descending in front. Aperture wide-lunate, oblique, the per- 

 istome expanded, reflexed ; columella short, nearly vertical, and 

 either convexly lobed or strongly toothed. The terminations of the 

 peristome are remote, joined by a translucent callus. , 



Most authors have included the If. cepoides Lea in Stylodonta. 

 That species is, however, far more closely allied to Cochlostyla, and 

 will be considered in connection with that group, in the next volume 

 of the MANUAL. The late Mr. Tryon (Man. Conch, ii, p. 26) in- 

 cluded Albers' group Erepta (type H. stylodon) as a synonym under 

 Stylodonta. This grouping is obviously unnatural, for the species of 

 Erepta do not exhibit the large embryonic shell nor the reflexed 

 peristome of the present group, and are besides wholly diverse an- 

 atomically, being correctly placed in the genus Nanina (sensu lati- 

 ore), whilst the true Stylodonta belongs to the Helicidce. 



Dufo's account of the reproduction of these snails is of the great- 

 est interest. He says of H. unidentata : " Sixty days after impreg- 

 nation the young are born. They lie in the oviduct one after an- 

 other, enveloped in a glairy mass, thicker at the aperture where the 

 head is. The animal of the mother is not protruded from the shell 

 during the birth of the young. After they have left the oviduct 

 they pass by their own movements out between the shell and 

 the body of the mother. There are usually two, rarely three ; 

 and in the latter event one of them is much smaller than the two 



