GENUS PLETJRECHINTJS, L. AGASSIZ. 451 



feroiis zoue. There is a distinct vertical row of primary tubercles 

 on the outer edge of the coronal plates, extending along the whole 

 length of the poriferous zone ; the rest of the ambulacral plate 

 is occupied by an inner and somewhat smaller tubercle, and an 

 irregular horizontal line of secondaries with miliaries extending 

 above the larger tubercle. The pores form very indistinct, irre- 

 gular, vertical arcs of three pairs ; the pores are separated by 

 slight ridges, and the miliaries of the coronal plates sometimes 

 encroach on the outer edge of the poriferous zone." 



The delineations of the apical system, and of some interradial 

 and ambulacral plates above the ambitus, are beautiful examples 

 af coi'rect art (Eeport on Echini, ' Challenger ' Expedition, 

 pi. x^ figs. 1,2). 



It will be noticed that in this description of the species and its 

 delineation there are no structures brought forward, or drawn, 

 which would ally the form with the Opechini. The generic 

 diagnosis requires, therefore, the abolition of the character of 

 possessing more than the normal number of horizontal sutural 

 depressions. Nothing is said, moreover, about the crenulation 

 of the primary tubercles, and the drawing shows them to be non- 

 crenulate. 



The carefully-described and well-drawn apical system, with its 

 circle of tubercles around the anus, and the depressions between 

 the ocular plates and this row of tubercles, are new features. It 

 is a truly Temnopleurid apical system ; and the truth of this 

 statement may be gleaned by examining young and old specimens 

 of Temnopleurus toremnaticus, and then referring to the apices of 

 the other recent species. A series of specimens of different 

 dimensions of Temnophurus toreumaticus, from the coast of 

 Cutcb, has been examined ; and I find considerable variation in 

 the ornamentation of the anal riug. But the depressions between 

 the ocular plates and the circle of tubercles, or, rather, between 

 the ocular plates and the junction of the generative plates, are 

 perfectly distinct in some, but not in other specimens. The only 

 distinction that can be drawn between the two forms is, that there 

 are more tubercles around the anus (and a tubercular ornamenta- 

 tion on the generative plates) in Pleureehinus hothryoides than in 

 the common Temnopleurus. However, there is a tuberculate 

 ornamentation in the other species of Temnopleurus on the plates. 

 The apical system of Pleurechinus will not, then, separate it from 

 Temnopleurus. 



