90 SVEN LOVEN, ON POTTUTALESIA, A GENUS OF ECHINOIPEA. 



ascends lengthwise 1 b 4, 5, 6, 4 a 4, 5, G, thus attaining 1 a. 6, 4 b il, and crosses I and 

 V at 11 or 12, and the odd interradiiim on its eighth pair of phites. 



With tlie evidently Schizasterian Aceste bellidifera for a guide it is not diffi- 

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

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

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

 frontal ambulacrum much less sunk, the peristome elabiatc 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 doi'sal; 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 same course, and the heteronomy of 1 appears t(j be 

 the same. It is likewise apetalous. 



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

 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 nouien trivinle, 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 ethmophraet calyx a general form like that of Collyrites ellip- 

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

 several plates. But it is provided with a peripheral fasciola, a feature Tiot 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 Pourtalesia hispida, Echino- 

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

 and P. carinata, Adete, Ethmopliract, Meridosternous and Apetalous, has its liivium 

 dorsally joining the calyx. 



Of the no less characteristic Urechinus Narcsianus Al. Ag. '), PL XXI, Jig. 239— 

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

 friends to whom 1 am oldiged for the inspection of duplicate specimens from the 

 ('hallenger Expedition. This species was brought up in the Southern Pacific and the 

 Antarctic from deptlis of 2500, 2G00, and 3300 metres, from 2926 m. in company with 

 i'durtah-sia hispida, P. carinata, Echinocrepis cuneata and Spatagocystis Challengeri, and 

 by the iSlake among the Lesser Antilla?, 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 surface almost flat, the interradium 5 slightly 

 rising and convex, the subanal part somewhat prominent; the peristome, fig. 240, is 

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

 buccial memlirane, wliich is covered with three circles of triangular scales, the outer- 

 most of which are l)y far the largest. The periproct, fuj. 241, rather wide, sul)-(irbicu- 



') Voy. Challenger I, .^80. Al,. Aoass, Rep. Cliall. Eeliin. p. 192, pi. XXXIII, XXXIII a. fi.?. 8—12. 

 '-) Voy. Chall. I, p. .-UIC. Ah. AtiAss. Rep. Clwill. Keliin. p. 1.5.5, pi. XXXIV. 



•') Report Chall. Eehiiioidca p. 14G, pi. XXIX, liy. 1—4. XXX, XXX a, lig. 1 — 14. R«port Hlakr Kehi- 

 iioidea. p. .52, pi. XXVI, W'j,. 1—.^. 



