456 BULLETIN OF THE 



ing 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 fine 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 

 five 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 ascer- 

 tain its affinities perfectly satisfactorily. As far as an examination 

 would allow, Keraiaphorus is identical with Ccelopleurus, and is 

 closely allied to Echinocidaris. There are some discrepancies between 

 the description of Michelin and his figures, the tubercles are not per- 

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

 plates is similar to those of Echinocidaris ; unfortunately the anal 

 plates are not preserved, and Michelin says nothing about them. 

 The peculiar structure 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-shaped curves across 

 this bare part of the interambulacra from the base of one plate to the an- 

 gle of the opposite plate, are quite prominent and fully as marked as in 

 the best figures of Ccelopleurus given by Cotteau in the Actes de la 

 Societe Linneenne de Bordeaux, pi. xii, fig. 4, Vol. 27. The spines 

 of Ccelopleurus are as yet not known, unless the spines cited under 

 the name of Cidaris incerta d'Arch, found in the same beds as those 

 containing Ccelopleurus, should turn out to be the spines of this genus. 

 They greatly resemble the smaller, shorter, and straight spines of Kerai- 

 aphorus found round the actinostome, as was suggested to me by Mr. 

 Vaillant of the Ecole des Mines.* 



In addition to the foregoing species, there was a small sea-urchin, one 

 eighth of an inch in diameter, which will most probably turn out to be 

 he young of some species of the Diadematidae allied to Asthenosoma 

 Grup.k. It is already of a .-i/.e when a young Diadema has its plates 

 tolerably well defined, and when its spines far surpass the diameter of 

 the test in length, besides being provided with a long anal proboscis, which 

 at once characterizes young Diadematidae. This specimen was nearly 

 flat, the outline deeply cut at the ambulacra, the interambulacra pro- 



• It i- interesting to note that we find a species of Ccelopleurus in the tertiaries of 

 Alabama, and in the Londen ( 



