SALENID^. 147 



M. Cotteau thus describes the family " Salenidees," Wright : — Pores disposed in single 

 pairs; ambulacra sometimes large, straight, and presenting a double range of small 

 tubercles ; sometimes narrow, and undulated, and garnished with granules ; interambu- 

 lacral tubercles few in number, largely developed, perforated, or imperforate, always 

 crenulated. Peristome sub-decagonal and furnished with entailles. Periprocte excentric 

 and posterior, placed in the axis of the animal or inclined a little to tlie right side. 

 Apical disc very large, solid, most often marked with deep depressions, composed of five 

 ovarial plates and five ocular plates perforated, with one or many sur-anal plates which 

 determine the excentricity of the periprocte. Madreporiform plate distinct, diSerent 

 from the others by its spongy aspect and sometimes by a simple laceration, a fissure more 

 or less large which corresponds to the genital pore and seems directed invariably to 

 the left side. The spines are sometimes elongate, aciculate, or sub-cylindrical, fm-nished 

 with fine longitudinal stria3 in the Acrosalenia heiuicidaroides, Wright, sometimes 

 enlarged, ovoid, sub-glandiform, more or less granular, as in the Pseudosalenia tuberculosa. 



The SaleniDjE are divided into two natural groups. 



1st. The Acrosalenia have narrow ambulacra gradually enlarged towards the oral 

 aperture and provided with perforated tubercles more or less developed ; the 

 peristome is divided into two lobes by deep incisions ; the apical disc is very large and 

 provided with a sur-anal plate composed of one or many elements ; in consequence of 

 the number of small sur-anal plates, and their feeble union with each other, they are 

 seldom preserved. 



2nd. The SalenicB, and the genera dismembered from them, have narrow ambulacra, 

 often undulated and garnished with tubercles; their peristome is feebly incised; the 

 apical disc is large and solid, projecting beyond the surface, and more or less deeply 

 marked with impressions at tlie sutures of the plates. 



The Acrosalenia: resemble Hemicidaris and llypodiadema, except in the sti'ucture 

 of the apical disc, and when this portion is absent it is often difficult to determine the 

 genus to which the mutilated specimen belongs ; but the great size of the discal aperture, 

 and the extension of the single ovarial plate into the single inter-ambulacrum readily 

 enable the trained eye of the observer to distinguish it from Hemicidaris. 



The SalenicB, on the other hand, resemble the CidariDvE by their narrow sub-flexuous 

 ambulacra, furnished with granules, their wide inter-ambulacral areas, their large primary 

 tubercles, and the inflated ovoid or sub-glandular spines, sometimes supported on them ; 

 their peristome is likewise feebly incised, like that of Cidaris. 



The Acrosalenice form only a single genus, the species of which, with one exception, 

 are distributed throughout the Jurassic rocks. 



The Siilenm have certain distinctive characters l)y which they are readily distinguished 

 from the Acrosalenice. 1st. Their tubercles are all imperforate, and 2nd, the position of the 

 vent, or periprocte, is always excentric and posterior; sometimes it is situated in the axis 

 of the body, and sometimes out of the axis, and inclines to the right side. For this reason 



