32 SVEN LOVEN, ECIIINOLOGIGA. 



crals is connected witli the fixed peristome by meaii.s of a tri- 

 angulär area with the two equal sides arclied, marked out by 

 numerous sunkeii spicules, large, fusiform or lanceolate, traiis- 

 verse, iinbricated adorally, arranged in two columns, mostly 

 smooth, while a limited number of tliem partly rise above tlie 

 membrane and thus form transverse ridges studded with ver- 

 rucules, spinules and forcipes, and disposed so as to represent 

 the ontlines of the area, in two marginal series, one mesial, 

 and two, less complete, intermediary. The narrow space be- 

 tween every two areas is interradial; its crowded spicules are 

 very minute near the peristome, then slightly increase, again 

 diminish, and between the primordial pairs pass into the 

 strong raised scales that fringe the buccal lips. The same 

 disposition obtains in the Echinothrix Diadema L.\ and is but 

 slightly diiferent in the Astropyga pulvinata Lamck in whicli 

 it was already seen by Al. Agassiz- In the Centrostepha- 

 nus coronatus Al. Ag., Fl. XII, fig. 154, the thin and trans- 

 parent buccal membrane is without any minute spicules, but 

 presents in the ambulacral areas large, linear, transverse la- 

 mels, mostly sunk and smooth, arranged to a certain order. 

 At the peristome there are on each side one large lamel, rai- 

 sed, tuberculated, emarginate for the gills; in the middle a 

 succession of narrow lamels, parallel, transverse, beginning 

 aborally with a mesial short one, foUowed by a roughly tri- 

 angulär set of gradually longer and more crowded imbricated 

 ones, out of which one or two in the middle and one on each 

 side near the primordial rise above the membrane and are 

 verruculated. 



The Aspidodiadema Antillarum Al. Ag., FL XII, fig. 155, 

 as already remarked by Al. Agassiz-^, is highly exceptional. 

 Adult specimens with large sexual apertures recall the post- 

 pluteal Cidaris, Fl. II, fig. 9. The ten paired primordials occupy 

 nearly alone the entire buccal membrane, they are large and 

 slightly wedge-shaped, heterotropic in size and imbrication, and 

 separated from the peristome by a very narrow interstice, in 

 which there are seen some few minute lamels. Thus in this 

 one genus of the Diadematidse the juvenile character of having 

 the calcified corona continuous from the raoutli to the calyx b\' 



' 1. c. p. 137. 



- Blake Eehinoidea p. 3"). 



3 Id. 1. p. 2'i, Pl. IX, fig. 5. 



