254 BULLETIN OF THE 



separating groups of species which are generally found closely allied. 

 From the study of young specimens I have been led to modify the views 

 I had taken of the nature of genera among Cidaridae, and as the group 

 requires a complete revision, I will not attempt at present to alter the gen- 

 era proposed in the Bulletin, hoping to make the changes in the general 

 revision of the order. With reference to Orthocidaris, to which this species 

 is temporarily referred, I would mention that, whether valid or not, the name 

 is preoccupied, having been employed by Cotteau a few months before the 

 publication of the Bulletin.* (The same is the case with Temnocidaris.) 



Test depressed ; the spines are not as distinctly fluted and crenated as 

 in C. hystrix ; they are often worn perfectly smooth, and attain their great- 

 est diameter at about one fifth the length of the spine from the base ; the 

 milled ring is finely striated, as well as the neck of the spine, which is sharp- 

 ly defined. The mamelon of the primary tubercles is small, deeply cut at 

 its base, high, the mammillary boss not prominent, the scrobicule deeply 

 sunk ; the scrobicular circle and interambulacral miliaries being prominent- 

 ly raised, the secondary tubercles of the scrobicular circle are but slightly 

 larger than the miliaries, diminishing regularly in size towards the sutures 

 of the plates, which are clearly and sharply cut; the same is the case with 

 the sutures of the ambulaeral plates ; each plate carries a larger exterior 

 tubercle with a smaller one nearer the abaetinal edge, and sometimes a 

 third and fourth miliary between the two. The poriferous zone is nar- 

 row, but slightly undulating and occupying half the ambulaeral plate. The 

 sutures of the plates of the abaetinal system are marked by distinctly cut 

 lines, instead of the wavy double line characteristic of C. hystrix; the abae- 

 tinal svstem is large, the ocular plates heart-shaped, the genital plates ir- 

 regularly octagonal ; the large sides of the plate adjoining the anal system 

 are separated by five long wedge-shaped anal plates, forming the base 

 of the smaller plates of the anal system. 



From 40 to 270 fathoms. 



Salenocidaris varispina A. Ag., nov. gen. et sp. 



The composition of the plates of the anal system in young Echini, ex- 

 plains most unexpectedly the homology of the sub-anal plate of Salenia, 

 and proves, from a different point of view, that the position of the anal 

 opening can in no wise form a guide by which we can determine any geo- 

 metrical axis of Echini, but that the only part of the abaetinal system which 

 has a constant structural relation to the axis is the madreporic body, which 



* Dnjardin and Iliipe refer its Mediterranean representative to Leiocidaris Des. 

 (PJiyllacanthua Br.), with which it has nothing in common, as the pores are, not joined 

 bv furrows. I would substitute for Orthocidaris Ac.nou Cott. the name Dorocidaris. 



