88 S. LOVEN, ON POURTALESIA, A OENUS OF ECHINOIDEA. 



at Avill pevhaps eome to thvow soiiic light upon the relations of certain fossil foi'ms 

 iiow regarded as characteristic of separate geological periods. 



Araong Archasonoinous genera, Goniocidaris, Aspidodiaderaa, Echinus are repre- 

 sented within the deep-sea habitats of the Pourtalesiada?, and along with them a few 

 littoral Spatangidas. Ainong the Prymnodesmians Kleinia, Maretia, Cionobrissus de- 

 scend to associate with Poui-talesia laguncula at depths of 630 and 1460 metres, and 

 well-known species of Brissopsis, Echinocardium, Spatangus, and a species of Maero- 

 pneustes, werc brought up from considerable depths by the Challenger and the Blake, 

 as also some genera and species unknown before. Linopneustes Murrayi Al. Ag. '), 

 found to live at 630 m. with Pourtalesia laguncula, has the elongated labriim and 

 short, angulate steimum of Mai'etia planulata, its episternum, its broad and naked 

 venti'al bivium with the three extended subanal plates, the same form of the plate 1 

 and 2-1-5 of the interradium 1, but its whole body is more convex, not so much ta- 

 pering posteriorly, the petals, level with the pei-isome, are more open and gradually 

 narrowing upward, and there is a narrow, peripetalous, peripheral fasciola of only 

 three or four minute tubercles in the transverse row. The two species of Homolampas "), 

 from 60 to 4500 metres, according to the figures and descriptions given by Al. Agas- 

 siz, also come near to Maretia, but the gradually narrowing petals are still more open, 

 their plates are much longer in relation to the breadth, and their pores are minute 

 and placed diagonally. Argopatagus Al. Ag. ''), an associate of Pourtalesia laguncula 

 at 1460 metres, to all appearance is not remotely akin to the foregoing, but apeta- 

 lous, the dorsal ambulacral plates being nearly equilateral hexagons with the pores al- 

 most central. Pala3otropus *), which lives in depths from 150 to 686 metres, is emi- 

 nently apetalous. 



Among the Prymnadetes the ancient Ethmophract genus Hemiaster descends from 

 300 to 1463 metres, and there joins Pourtalesia laguncula. The Ethmolysians are 

 represented by two very remarkable forms of the group of Schizaster. 



Aceste bellidifei'a Wyv. Thoms. °) appears to be a true deep-sea form, its habi- 

 tats being at 3500 and 5000 metres, the last shared with Pourtalesia rosea. Thanks 

 to Mr John Murray I can give, from actual observation, a description of its skeleton, 

 Pl. XX. The pedicels have been described above, j9. 53, Pl. X, fig. 96 — 98. In the 

 dorsal aspect the outline of the body is ob-cordate, frontally drawn in so as to form 

 a deep sinus, continuous with the large, bi'oadly lanceolate depression that occupies 

 the middle part of the anterior slope. The dorsal surface gradually rises backward to 

 far beyond the middle; then the calycinal system, for a small apical space, is horizon- 

 tal, the part behind it declining into the almost abruptly vei'tical, high, nearly flat, ellip- 

 tical anal surface. The ventral side, level along the middle line, posteriorly suddenly 

 bends upward at the suture between the stei"num and the episternum ; latei'ally it 



') Eep. Chall. Ecliin., p. 167, pl. XXV, XXV b. 

 "-) Ib., p. 164, pl. XXIV. 

 3) Ib. p. 160, pl. XXII, fi^. 1— G. 

 ^) Études, pl. XXXII, fio-. 200. 



'") Voy. Challenger, I, p." 376. — Al. Ag., Rep. Chall. Eohin., p. 195, pl. XXXIL fig. 7— 11, XXXIII, a, 

 lig. 1—7. 



