Th<ii<s.\ GASTROPODA. 421 



KEY TO GENERA. 



A. Whorls .spirally ridged, the ridges sometimes nodulous ; aperture 



wide ; outer lip crenate or lightly denticulate ; siphonal canal 



absent or short . . . . . . . . . . . . THAIS. 



B. Whorls tubercular or spinose ; aperture narrow ; outer lip with 



strong teeth within ; columella wrinkled or plicate . . . . DRUPA. 



Genus 1. THAIS, Bolten, 1798. 



Thais, Bolten, Mus. Bolten., 1798, 54. First species : Purpura neritoides, 

 Lamarck. Purpura, Lamarck, 1799 ; not of Martyn, 1784. Lepsin, 

 Hutton, 1884. (For full synonymy, see W. H. Dall, U.S. Geol. Survey, 

 Professional Paper 59 ' The Miocene of Astoria and Coos Bay, Oregon," 

 1909, 46.) 



Animal with a short foot, truncated in front ; head small and broad ; 

 tentacles long, with the eyes on the outer side near the anterior third. 

 Radii la long, the central tooth with 3 principal cusps and a few marginal 

 denticles on each side ; laterals claw-shaped. 



Shell solid, ovate or suborbicular, more or less turreted, body- 

 whorl very large ; surface sculptured with striations or sulcations, 

 usually spirally, often forming fimbriated ridges, and sometimes broken 

 up into nodules or tubercles ; fascicle more or less prominent ; aper- 

 ture ovate, dilated, notched or with a short canal below ; outer lip 

 crenated or denticulated ; columella flattened, callous, sometimes sub- 

 excavated. 



Distribution. About 60 species are known ; they are found in 

 most seas, but the maximum occurs in the tropics. 



Fossil in the Tertiary. 



Vernacular Name. Dog-winkle. 



KEY TO SUBGENERA. 



A. Shell without a siphonal canal, simply notched . . . . THAIS. 



B. Shell with a rudimentary canal, columella nearly straight, 



slightly twisted below . . . . . . . . STRAMONITA. 



C. Shell with a recurved canal and prominent fascicle, columella 



strongly twisted below, separated from the fascicle by an 



umbilical depression . . . . . . . . NUOELLA. 



Subgen. 1. THAIS, s. str. 



Type : Ptirpurn neritoides, Lamarck. 



Animal as in the genus. Dentition 1+J + l. the middle cusp of 

 the central tooth very long, the middle side cusps small, and the lateral 

 cusps larger ; marginal teeth long and pointed. 



Shell oblong-oval, whorls smooth ; last whorl very large, the 

 aperture occupying three-fourths of the height of the shell ; spire 

 short ; aperture ovate ; columella flattened ; outer lip lirate within. 



