90 SVEN LOVEN, ON PdlTRTALESIA, A GENUS OF EOIIINOIDEA. 



ascends lengthwise 1 b 4, 5, 6, A a 4, 5, 6, thus attaining 1 a S, 4 b 6, and crosscs I and 

 V at 11 or 12, and the odd interradiura on its eighth pair of plates. 



With the evidently Schizasterian Aceste bellidifera for a guide it is not diöi- 

 cult to see the afiinity, though distant, of the very extraordinary Aerope rostrata 

 Wyv. Th. '), another inhabitant of the great depths, from 1460 to 3200 metres. Ac- 

 cording to the figures and descriptions given, its body is inuch more elongate, the 

 frontal ambulacrura much less sunk, the peristome elabiate and subcircular, not anterior, 

 but ventral, at the third of the entire length; the labrum is very long, the sternum 

 occupies the posterior third, the periproct is dorsal; the calycinal system has four 

 sexual pores; the madreporite is central. The pedicels of III are those of Aceste and 

 Schizaster, the fasciola has the sanae course, and the heteronomy of 1 appeai"s to be 

 the same. It is likewise apetalous. 



Recent Echinoids coming near to the earliest Spatangida3, Adete, Ethmophract, 

 Meridosternous, were unknown to science, and indeed do not seem to exist in the 

 littoral belt. It was the good fortune of the late Sir Wyville Thomson to bring to 

 light, near Fayal, from a depth of 4850 metres the very singular Calymne relicta ^), 

 and to have to indicate, by a nomen triviale, the significance of the discovery. It 

 looks indeed like a relic from the Older Cretaceous or even the Oolitic period, com- 

 bining with a perfectly ethmophract calyx a general form like that of CoUyrites ellip- 

 tica or ovalis, a bivium widel}' separated from the calyx, a sternum composed of 

 several plates. But it is provided with a peripheral fasciola, a feature not foreign, it 

 seems, to Cardiaster. It is apetalous. Its near ally, Cystechinus Al. Ag., a deep-sea 

 form from 1900 to 4070 metres, at 2900 m. an associate of Poui-talesia hispida, Echino- 

 crepis and Spatagocystis, at 3950 m. of P. ceratopyga, at 4070 m. of that species 

 and P. carinata, Adete, Ethmophract, Meridosternous and Apetalous, has its bivium 

 dorsally joining the calyx. 



Of the no less characteristic Urechinus Naresianus Al. Ag. ^), Pl. XXI, fig. 239 — 

 242, I can speak from direct observation, thanks to the liberality of my English 

 friends to whom I am obliged for the inspection of duplicate specimens from the 

 Challenger Expedition. This species was brought up in the Southern Pacific and the 

 Antarctic from depths of 2500, 2600, and 3300 metres, from 2926 m. in company with 

 Pourtalesia hispida, P. carinata, Echinocrepis cuneata and Spatagocystis Challengeri, and 

 by the Blake among the Lesser Antillae, from 772 and 2200 metres. In the dorsal 

 aspect its outline is oviform, tapering behind, the surface entirely smooth, the calyci- 

 nal system nearly central; the ventral sux'face almost flat, the interradium 5 slightly 

 rising and convex, the subanal part soniewhat prominent; the peristotne, fig. 240, is 

 slightly sunk, sub-pentangular, with the small oesophageal opening in the centre of the 

 buccal membrane, which is covered with three circles of triangulär scales, the outer- 

 most of which are by far the largest. The periproct, fig. 241, rather wide, sub-orl^ien- 



•) Voy. Challenger I, 380. At,. Agass. Rep. Clmll. Echin. p. 192, pl. XXXIII, XXXIII a, %. 8—12. 

 -) Voy. Chali. I, p. 39G. Al. Agass. Rep. Chall. Echin. p. L^S, pl. XXXIV. 



^) Bepoi-t Chall. Eehinoidea p. 14G, pl. XXIX, lig. 1—4, XXX, XXX a, fig. 1—14. Report Blake Eehi- 

 iioidoa. p. 52, pl. XXVr, lig. 1—3. 



