(70 S- ^'OTo : 



• 



" When these tlu-ee species are compared inter sc it is (îvident that iu 

 many respects Cienodiscvs corniculatvs, though so AvidiJy separated geo- 

 gi-aphicall}-, appears to occupy an intermediate classificatory position between 

 Ctenodiscns mistrah's and Cienodiscvs procurator, whicli inhabit the eastern 

 and western sides res]oectively of South America. In Ctenodiscvs procurator 

 the rays are generally a trifle longer, and, even when not actually so, have 

 at least that appearance iu consequence of being slightly narrower at the 

 base and more attenuate and ^jointed out^Nardl}'. The abactinal area is 

 pLxne, its union -with the lateral A\'all, especially in the region of the disk 

 and the base of the rays, forming a sharp angle in consequence of the 

 rapid adorai slope of the whole lateral -wall ; the supero-marginal plates 

 being also aflected iu the majority of cas(is. This feature at once strikes 

 the ej'o in compaiisou witli the usually ^'(^rtical and actinally well-rounded 

 margin of Ctenodiscvs eorniculatus and the thick and tumid one of Ctenodiscus 

 avstralis. 



" The x^fi^xiUie of the abactinal area ave small and croAvded, similar to 

 those in Ctenodiscvs cornicvlatv.s. The madreporiform body is distinct and 

 not lüdden by paxiUae as in Ctenodiscus australis. The marginal plates a]}- 

 pear to be invariably rather more numerous than iu Ctenodiscvs eorniculatus, 

 and consequently still more so than in Ctenodiscvs australis ; — for (example, 

 in a specimen of Ctenodiscvs procurator, measm-ing 11 = 28.5 nun., there are 

 eighteen supero-marginal plates coimting from the median interradial line 

 to the extremity ; whereas in Ctenodiscus eorniculatus of exactl}- the same 

 radial dimensions (R=:28.5 unn.) there are only fifteen. Ctenodiscus 

 eorniculatus, with R = 27mm., has foui-tet-n supero-marginal plates; Ctenodis- 

 cus procurator, Avitli 11 = 27 mm., has seventeen. Ctenodiscus procurator a.i>- 

 peal's to have generally ouo or more spines less on the adambulacral plates 

 than iu Ctenodiscus eorniculatus, tlnee only being actually marginal or 

 fmToAv spines, and n ftjui-th standing backward and on the actinal 

 surfac(i of tlu^ plate at the aboral end. Yery rarel}' indcuid are fom* 

 fuiToAN' spines ])resent ; whereas four and five are general in Ctenodiscus 

 eorniculatus. 



"From the foregoing r(imarks it will be seen Wii\X, Ctenodiscus procurator 



