RICINULA. 183 



difficult to trace, and I have seen worn specimens of either of 

 those genera which might be readily referred to the others ; on 

 this account some species originally described under Sistrum I 

 have been able to refer definitely to other groups ; whilst others, 

 from Insufficiency of diagnosis, illustration or specimens are 

 retained, but with doubt. The genus is essentially Polynesian 

 in distribution, frequenting coral reefs. 



R. HYSTRIX, Linn. PL 5(>, tig. 195. 



The surface varies from nodulous to spinose ; in very large 

 specimens the shell is sometimes umbilicate. Yellowish brown ; 

 the interior of aperture rich rose-color. 



Length, T5-2-5 inches. 



Sandwich Isles : Fiji Isles ; Paunwtus. 



lu this, the largest species, the teeth have but little disposi- 

 tion towards grouping. 



Var. REEVEANA. Crosse. PI. ."><;. tig. 19C>. 



The surface is nine- varicose instead of seven-varicose -as in H. 

 clathrata. Lam. The interior of the aperture is violet-purple. 

 I do not find the distinction in the number of varices to hold 

 good, as 1 have before me specimens of the latter with as many 

 as ten varices. The interior of the aperture is less rugose upon 

 lip and columelln, and wants, besides, the brown markings of 

 clathrafd. 



Marquesas Isles. 



Var. SPEU10SA. Dunker. PI. 5(J, fig. 194. 



Small, rugosely tuberculose. the tubercles prominently arranged 

 in revolving series ; columella strongly four-plicate. 



Length, '83 inch. 



Rarotonga, Paumotus. 



This is a w r ell marked variety, distinguished by its small size, 

 very deep rose-purple interior, columellar plaits, etc. It was 

 first figured by Reeve as VMT. of //. clathratn, Lam., and then 

 described by Dunker. Subsequently, the latter finding Reeve "s 

 figure cited as the young in Oosse's description of fieeveana, 

 abandoned his species as synonymous with that of Crosse. I 

 consider the two to be well distinguished varieties, diverging in 

 opposite directions from the type*. 



