STYLODONTA. 149 



jaw strong and ribless ; all of the teeth of the radula unicuspid ; the 

 genital system without flagellum on penis and with no dart sac or 

 mucous glands on vagina. To these characters we may add that 

 the transverse rows on the radula are moderately straight (not V-- 

 shaped), the basal-plates of all the teeth are of the usual quadrate 

 form, and the large embryonic shell is usually sculptured differently 

 from the after-growth. The shell never has teeth or folds in the 

 aperture, although the columella shows often a long spiral, produc- 

 ing a visible sinuosity or truncation below, which, incidentally, in 

 some depressed forms, is shortened into a tooth-like columellar pro- 

 cess. 



The affinities of the genera Plectopylis and Gorilla may be with 

 this phylum, but if so, the connection is so remote or so much ob- 

 scured by special modifications, that they may better be left isolated 

 until more fully understood. The Adams brothers, Try on, Fischer 

 and others, guided by certain analogies in the shells, have classified 

 these Indian genera with the American Polygyras and the Eur-Asian 

 Gonostomas, but the group so constructed is shown by a study of 

 the soft parts to be a house built upon the sand. 



Genus STYLODONTA Crist, and Jan, 1832. 



Stylodonta DE CRISTOF. et JAN., Catal. p. 2, type H. unidentata. 

 PILSBRY, Man. Conch., vi, p. 85. Stylodon BECK, Index Moll., 

 p. 46. ALB.-MART., Die Hel., p. 149 (in part). Columplica 

 HARTM. (part) Gast. Schweiz, p. 187. Pachya ALB., Die Hel., p. 

 107 (in part). For anatomy see W. G. BINNEY, Ann. N. Y. Acad. 

 Sci., iii, p. 110 (teeth and jaw of Studeriana). VIGUIER, Arch. 

 Zool. Exper. et Generale, viii, p. 529, pi. 40 (genitalia of Studeriana). 

 SCHACKO, in Mobius' Beitr. zur Meeresfauna Maurit. u. Seychellen, 

 p. 342 (anatomy of unidentata}. MARTENS in v. d. Decken's 

 Reisen in Ost-Afrika, iii, i, p. 56, pi. 1 (varieties of unidentata). 

 NEVILL, P. Z. S., 1869, p. 61 (conditions of snail life on Seychelles). 



Shell depressed- turbinate, solid, with imperforate axis at all stages 

 of growth ; obtuse apex ; and keeled periphery, at least in the young. 

 Surface yellowish or dark brown ; whorls 5, the earlier 3 spirally 

 grooved or decussated, forming an embryonic shell about one-third the 

 diameter of the adult ; outer whorls finely wrinkled, the last descend- 

 ing in front. Aperture wide-lunate, quite oblique, the peristome 

 expanded or reflexed. Columella short, subvertical, its inner edge 

 with a convex lobe or a sharp tooth-like fold. Type, S. unidentata, 

 pi. 38, fig. 9. 



