268 COELOPLEURUS FLORIDANUS. 



cave part of the spine, and a light pink on the opposite side ; the extremity 

 of the spine is white for a considerable distance; the spine is slightly 

 curved from the base; a section of the spines (PI. IP. f. 15) shows them to 

 be somewhat triangular, with rounded sides, the long convex side of the 

 triangle being placed on the side of greatest diameter of curvature of the 

 spine, and the short slightly concave or straight sides on the concave part 

 of the spine. The spine is nearly solid, with the exception of a small annu- 

 lar space, nearer the centre than the periphery, made up of one row of 

 large triangular limestone cells, such as are so characteristic of spines of 

 Echini; the central part and the periphery of the spine consist of very 

 minute circular cells, similar to those of Cidaris spines, closely packed 

 together, presenting a homogeneous structure ; in consequence, the outside 

 of the spine is not striated, either longitudinally or transversely, and shows 

 simply a homogeneous close granulation, like very line marble. The 

 longest fragments are about two inches in length, and, to judge from 

 analogy with Keraiaphorus Maillardi, they must have attained a length of 

 at least live or six inches. It is to be hoped that future explorations will 

 bring to light this interesting Sea-urchin, as the only specimen thus far 

 found is not in such a state of preservation as to enable us to ascertain its 

 affinities perfectly satisfactorily. 



As far as an examination would allow, Keraiaphorus is identical with 

 Coelopleurus, as had already been suggested by Liitken. it has t lie same 

 abactinal system, the broad ambulacra! zones compared with the interambu- 

 lacral area, though not quite so sunken as in the fossil species. The arrange- 

 ment of the pores is the same in arcs round the base of the primary tuber- 

 cles; the genus is closely allied to Arbacia. There are some discrepancies 

 between the description of Michelin and his figures: the tubercles are not 

 perforated nor crenulated, the general structure of the genital and ocular 

 plates is similar to those of Arbacia ; unfortunately the anal plates are 

 not preserved, and Michelin says nothing about them. The peculiar struc- 

 ture of the bare portion of the abactinal part of the interambulacra is not 

 sufficiently brought out in Michelin's figures ; in the specimen, ridges of 

 small tubercles, running in S-shapcd curves across this bare part of the 

 interambulacra from the base of one plate to the angle of the opposite plate, 

 are quite prominent and fully as marked as in the best figures of Coelo- 

 pleurus given by Cotteau in the Actes de la Societe Linneenne de Bordeaux, 

 PI. XII. f. J f , Vol. XXVII. The spines of Coelopleurus are as yet not known, 



