86 HELIX-STYLODONTA. 



others. During the period of gestation the animal becomes thin, 

 having lost over a half of its volume by the end of that time. I 

 have always noticed that those individuals having shells of a less 

 dark color are the only ones bringing forth young." The same ob- 

 servations apply to H. studeriana also. This species, however, bears 

 only one or two young at a time. 



H. UNIDENTATA Chemnitz. PL 61, figs. 21, 22. 



Shell depressed, imperforate ; spire low-conoidal, blunt ; body- 

 whorl keeled ; aperture very oblique, the short vertical columella 

 with a strong, acute, twisted tooth. 



The shell is solid, strong and opaque, of a chestnut-brown color all 

 over, sometimes yellowish-brown ; the surface is slightly shining, the 

 inner 3J whorls very minutely granulated and marked by impressed 

 spiral lines ; the following whorls lightly marked by growth-lines 

 and covered with fine, close, obliquely descending wrinkles ; this 

 corrugation is often almost obsolete above, but is always distinct be- 

 low the periphery. A strong lens reveals a microscopic decussation 

 over all the coarser sculpture, like that described under H. studeriana. 

 The spire is elevated-dome-shaped ; the suture superficial at first, be- 

 coming impressed around the last volution. The body-whorl is 

 acutely keeled at its origin, but becomes more rounded at periphery 

 as it approaches its termination. It descends below the peripheral 

 keel in front. Aperture very oblique, broader than high, flesh- 

 colored or livid-brown inside ; peristome narrowly expanded, thick- 

 ened within ; columella short, vertical, formed of a strong, acute 

 fold. 



Alt. 33, greater diam. 49, lesser 42 mill. 



Alt. 27, greater diam. 41, lesser 35 mill. 



Alt. 24, greater diam. 34, lesser 29 mill. 



Make, Silhouette, etc., Seychelles Islands. 



Helix unidentata CHEMNITZ, Syst. Conchyl. Cab. xi, p. 273, t. 

 208, f. 2049, 2050. FER., Histoire, t. 104, f. 8, 9. PFR., Mono- 

 graphia i, p. 303 ; Conchylien Cabinet, p. 30, t. 2, f. 6, 7. DUFO, 

 Ann. Sci. Nat. xiv, p. 199, 1840. SCHACKO, in Beitriige zur Meeres- 

 fauna der Ins. Mauritius und der Seychellen, p. 342, 1880 (Anat- 

 omy). REEVE, Conch. Icon., t. 39, f. 156. Nanina (Stylodonta) 

 unidentata Chem., TRYON, Manual of Conchology ii, p. 26. H. mi- 

 crodonta DESK., Encyc. Metli. ii, p. 266. H. ventricosa JAN, Man- 

 tissa, p. 1. Columplica uniplicata HARTM. Gastrop. Schweitz i, p. 187, 



