330 SUBFAMILY CCELIAXIN^. 



The summit of a young specimen is drawn, pi. 47, fig. 23, 

 to show the slight distortion at the junction of the embryonic 

 with the neanic stage, accompanied by a change in the direc- 

 tion of the striae. This shell is more distinctly striate than 

 the larger one figured. The name L. martensi is preoccu- 

 pied, but pending a thorough inquiry into the status of the 

 Cocos Island forms, no change is advisable. 



Subfamily CCELIAXIN^ Pilsbry. 



Cylindric or turrite, narrow, many-whorled forms, with the 

 axis hollow (except in Cryptelasmus), and the cavity of the 

 whorls obstructed by lamellae on the axis, parietal wall and 

 sometimes the basal wall. Dentition Achatinoid. 



This subfamily is composed of a few very distinct genera, 

 all of them at present monotypic. Widely scattered, yet each 

 is restricted to an excessively small area. It would seem to 

 be a group evolve.d in Mesozoic time and now approaching 

 extinction. The several genera were first associated by the 

 author in 1904 (Man. Conch., xvi, p. 194). 

 I. Shell imperforate, its axis slender and solid; oviparous; 



American. 



a. Shell very slender, sinistral, turrite with cylindric 

 summit; composed of 11-15 narrow whorls, one or 

 two intermediate whorls obstructed by a parietal 

 and two axial lamellae ; aperture oblique, ovate, with 

 a parietal lamella. Genus CRYPTELASMUS Pils. 



II. Shell perforate or umbilieate; viviparous; Eur- African. 

 a. Shell with 12-13 whorls, the initial 3y 2 forming a 

 narrow, subcylindric summit; last two whorls with 

 an axial and a parietal lamella, the latter continued 

 to the aperture; outer lip simple and thin. Island 

 of St. Thome, in the Gulf of Guinea. 



6. Axis perforate. Genus THOMEA Girard. 



66. Axis openly umbilicate. 



Genus PYRGINA Greef . 



aa. Shell tapering-cylindric, ribbed, with a peripheral 

 and a basal keel on the last whorl, the latter bound- 

 ing an open umbilicus; outer lip with a collar-like 

 rib; cavity of last whorl with axial and palatal 

 lamellae and a basal fold. Eocene, Paris Basin. 



Genus DISTCECHIA Crosse. 



