4 SVEN LOVEN, ON A KECENT FORM OF THE ECHINOCONID^. 



Eacli ambulacrum begins in the peristome with botli its 

 first plates, Pl. 1, fig. 2, 5. Of each of tliese the one half 

 that bears the pore is free, more than twice as long as it is 

 broad, and slightly expanding aborally. In the I a, II a, III b,. 

 IV a, V h it is longer than in the I h, II h, III «, IV h^ \ a,, 

 in conformity with the general Echinoidean formiila. These- 

 first ambulacrals are followed by an iminternipted double se- 

 ries of simple and depressed plates, twice to thrice as broad 

 as they are long, which attain their greatest breadth at the 

 ambitus, and from thence are regularly contracting up to the- 

 calyx, being there sligthly sunk, jig. 6. The geminous pores,. 

 single even in the large peristomal plates, then follow closely 

 one upon another, and thus form a simple, straight, slightly 

 impressed series from the peristome to the calyx. The peri- 

 podia, pg. 4, 7, 10, are sunk, oblong, contracting inwards; the 

 external perforation is round, the inner one a slit, conlinent 

 with it and apparently withont auy septum; near the peri- 

 stome it is directed almost adorally, then diagonally, and at 

 the ambitus and upwards nearly transversely. The outer la- 

 teral halves of the two peristomal ambulacrals each of them 

 support an aniicle, fig. 2, 5, *, *♦, presenting a longitudinal^ 

 slightly convex surface, low and rather narrow at the peri- 

 stome, gradually rising and expanding aborally, its prominent 

 free extremity reaching as far as up to the third or fourth 

 plate. Each auricle diverges a little aborally from that of the 

 other plate, and overhangs laterally the adjoining interradium,. 

 so as to produce tlie appearance of belonging to it. In the 

 speciraen the auricles of I b, IV a and V a have fallen off, 

 and have left their bases alone remaining, fig. 5 *♦. 



The peristomal margin has the appearance of being dou- 

 ble, fi,g. 7, 4, and to consist of an interiör, faintly prominent 

 lip, and another exteriör somewhat retreating. The former,^ 

 which cannot be seen as shown in fig. 7 unless in a strongly 

 leaning position of the stoma, is thin, and presents in each 

 ambulacrum two deep and narrow incisions whicli, when seen 

 from the interiör, fig. 5., appear as mere linear cuts just out- 

 side the auricles. The exteriör lip is tumid, especially at 

 each ambulacrum, from two ovate, transverse, contiguous pro- 

 tubcrances, fig. 7. Just behind these, in the middle, a circular 

 hollow indicates the former existence of a spherid now löst, 

 the position of which is marked by a very minute tubercle 



