544 trochidjE. 



very difficult, if possible, to draw a line between the two 

 groups. Until, however, the animal of Scissurella be better 

 known, and the Pleurotomaria, at present probably uniting 

 creatures of different families, better investigated, it would 

 be unsafe to merge the two genera in one. 



S. crispata, Fleming. 



Plate LXIII. fig. 6. 



Scissurellu crispata, Flem. Mem. Wern. Soc. vol. vi. p. 385, pi. 6, f. 3 ; Brit. 

 Anim. p. 3G6 ; Treatise Moll. Anim. pi. 13, f. 48.— Brit. 

 Marine Conch, p. 152.— Brown, Illust. Conch. G. B. p. 62. 



A more extended knowledge of the influence of climate 

 upon form, as well as sculpture, may greatly enlarge 

 the synonymy of this minute and beautiful shell ; for 

 assuredly several of its congeners approach it most 

 closely in general characters. It is thin, semitranspa- 

 rent, of a pure and uniform white, and, in the individuals 

 we possess (yet these probably are dead specimens), but 

 little shining. The shape is obliquely suborbicular, and 

 more produced at the base than at the spire ; the lateral 

 outlines of the upper disk are convex. The sculpture, 

 which is very elegant, and enriches alike the entire super- 

 ficies, consists ' of a crowded decussation of delicate longi- 

 tudinal and spiral laminar striee, both series being narrower 

 than the intervals between them. The latter, which are 

 chiefly visible in the interstices, and are rather the more 

 minute, produce a crisp or slightly curly appearance 

 where they intersect the others. A broad spiral groove, 

 with raised edges, that terminates in a rather long fissure, 

 winding along the bases of the smaller volutions, and encir- 

 cling the body just above the middle, interrupts the graceful 

 curves of the longitudinal striae, and produces a divarication 



