REPORT ON THE ASTEROIDEA, 173 
3. Ctenodiscus procurator, n. sp. (Pl. XXX. figs. 7-12). 
This form has so many points of close resemblance to the North-Atlantic Ctenodiscus 
corniculatus that examples might be selected which at first sight would easily be 
mistaken for that species. A number of small differences, however, present themselves 
when a large series is examined, which appear sufficiently constant to warrant the recog- 
nition of this form as a distinct species. Under these circumstances the description of 
Ctenodiscus procurator will probably be most intelligible if it takes the form of a com- 
parative review of the characters of this species in relation to those of the two previously 
known species of Ctenodiscus, viz., Ctenodiscus cornmiculatus of the North Atlantic, and 
Ctenodiscus autralis, Liitken, from the East of Patagonia. 
When these three species are compared inter se it is evident that in many respects 
Ctenodiscus corniculatus, though so widely separated geographically, appears to occupy 
an intermediate classificatory position between Ctenodiscus australis and Ctenodiscus 
procurator, which inhabit the eastern and western sides respectively of South America. 
In Ctenodiscus procurator the rays are generally a trifle longer, and, even when not 
actually so, have at least that appearance in consequence of being slightly narrower at 
the base and more attenuate and pointed outwardly. The abactinal area is plane, its 
union with the lateral wall, especially in the region of the disk and the base of the rays, 
forming a sharp angle in consequence of the rapid adoral slope of the whole lateral wall ; 
the supero-marginal plates being also affected in the majority of cases. This feature at 
once strikes the eye in comparison with the usually vertical and actinally well-rounded 
margin of Ctenodiscus corniculatus and the thick and tumid one of Ctenodiscus australis. 
The paxillze of the abactinal area are small and crowded, similar to those in Cleno- 
discus corniculatus. The madreporiform body is distinct and not hidden by paxilla as in 
Ctenodiscus australis. The marginal plates appear to be invariably rather more numerous 
than in Ctenodiscus corniculatus, and consequently still more so than in Ctenodiscus 
australis ;—for example, in a specimen of Ctenodiscus procurator, measuring R=28°5 
mm., there are eighteen supero-marginal plates counting from the median interradial line 
to the extremity ; whereas in Ctenodiscus corniculatus of exactly the same radial dimen- 
sions (R=28°5 mm.) there are only fifteen. Ctenodiscus corniculatus, with R= 27 mm., 
has fourteen supero-marginal plates; Ctenodiscus procurator, with R=27 mm., has 
seventeen. Ctenodiscus procurator appears to have generally one or more spines less on 
the adambulacral plates than in Ctenodiscus corniculatus, three only being actually 
marginal or furrow spines, and a fourth standing backward and on the actinal surface 
of the plate at the aboral end. Very rarely indeed are four furrow spines present ; 
whereas four and five are general in Ctenodiscus corniculatus. 
From the foregoing remarks it will be seen that Ctenodiscus procurator is much more 
closely allied to the North-Atlantic Ctenodiscus corniculatus than to the comparatively 
neighbouring form Ctenodiscus australis, from which it is readily distinguished, On the 
