430 EUCHELUS. 



mella with a tooth near the base, sometimes a notch below it. 

 Huttonia Kirk, is synonymous. 



HERPETOPOMA Pilsbry. Shell turbinate-conic, etc., as in Euchelus ; 

 spire elevated ; operculum multispiral as in typical Trochus. Type, 

 E. scabriusculus Ad. 



HYBOCHELUS Pilsbry. Shell depressed, with very short spire and 

 large body-whorl ; outer lip not thick; columella simply concave, 

 not in the least toothed or notched, somewhat refiexed above ; oper- 

 culum unknown. Type, E. cancellatus Krauss. 



The sculpture in Euchelus consists of spiral ribs crossed by ele- 

 vated striae, which bead them and cut the interliral furrows into 

 pits, or frequently are nearly obsolete in the furrows. The spirals 

 increase in number by the interpolation of tiny interstitial riblets, 

 which increase in size until they become equal to the primary 

 spirals. It follows that a species having equal ribs on the last part of 

 the body-whorl, has alternately larger and smaller ones on the 

 penultimate whorl, and usually equal ones again on the next 

 earlier. Species like Euchelus principalis, with numerous equal 

 riblets in the adult, have fewer unequal ones when young. The 

 imperforate forms are always (so far as I know) decidedly um- 

 bilicate when young. The above remarks on the development of 

 spirals apply to most forms of Trochids in which each interstitial 

 furrow gives rise to a single secondary riblet ; those forms which 

 develop numerous spiral striae in each inter-liral space (Clanculus 

 plebeius, Chlorostoma maculostriatum, etc.), will always be found to 

 be excessively variable in the number of more prominent spirals. 

 There are other forms, as Calliostoma lima, in which there are three 

 or four orders of spirals; for example, the 1st, 5th, and 9th lirse 

 may be largest and equal ; the 3d and 7th smaller, 2d, 4th, 6th, 8th 

 still smaller. These species, following a certain mathematical 

 method, are somewhat constant. It only remains to note those like 

 Perrinia elisa, P. maculata, etc., which have the same number of 

 spirals on all the whorls, no interstitial riblets being developed. 

 In these the number of spirals is very characteristic. 



Section EUCHELUS s. s. 

 E. QUADRICARINATUS Chemnitz. PI. 38, figs. 9-11. 



Shell globose-conic, imperforate, strong, solid, pinkish fawn-colored 

 with numerous obliquely descending black stripes, often broken into 

 dots. Spire short, conic ; sutures impressed ; whorls 5, rounded, encir- 



