.S6 S. LOVEN, ON I'OUHTALIiSIA, A GENUS (IF ECIUNUIDEA. 



tlireu liabitats, iii. d. 3500 in.; P. cci'atopyjjfn, three habituts, ui. d. 3800 iii.; P. rosea 

 at 4750 in.; Echiiioerepis cuiieata at 2900 m.; Spatagocystis Clialleugeri, two lKil)itats, 

 in. d. o250 111., the inediuni of their average depths being 3800 metres. Above the gene- 

 ral niediuni deptli of 2900 metres and up to 442 m., from the Globigerina ooze to 

 the sandy mud mixed with pebbles, were found two species: Pourtalesia Jeffreysi, in 

 four habitats, at a mean depth of 1300 metres; P. miranda, two habitats, m. d. 1200 

 m.; and one species alone, Pourtalesia laguncula, from 630 m., sandy mud, 5° C, 

 down to 5303 m., red clay, 1° C, in five habitats, mean depth 3000 metres. At one 

 locality, in the Antarctic ocean, half-way between the Cape and Kerguelcn Island, at 

 a de[)th 292G m., four species wei'e found living together at one locality, Pourtalesia 

 his[)i(la, P. carinata, Echinocrepis cuneata. Spatagocystis Challengeri; half-way between 

 Kerguelcn Island and South Australia, in one locality, depth 3576 m., three species, P. 

 cerato[)yga, P. carinata, Sp. Challengeri were found with one another; two species, P. 

 phiale and P. hispida not far from there, at more tlian 62° S., depth 3611 m.; and 

 two others, P. ceratopyga and P. carinata near the coast of Chile, at 4069 m. The 

 rest were found single. 



Thus, as far as our present knowledge goes, three species are Atlantic, and one 

 of these also Antarctic; two were found in the Pacific and live in the Antarctic Sea; 

 and of the ten species hitherto known none comes nearer to the surface than by 442 

 metres, while two descend to 1000 and to 2000 in., one to near 3000 m., three to 

 between 3000 and 4000 m., three to between 4000 and 5000 m., and one to beyond 

 5000 meti'es. 



The littoral region comprises the favoured zones of the sea, Avhere light and 

 shade, a genial temperature, currents changeable in power and direction, a rich vegeta- 

 tion spread over extensive areas, abundance of food, of prey to allui'e, of enemies to 

 withstand or to evade, represent an infinitude of agents competent to call into play the 

 tendencies to vary, definite in kind and limited in number, which are embodied in each 

 species, and always ready by modifying its parts to respond to the influences of external 

 conditions. In this region the great majority of marine forms are at home, of the Echi- 

 noidea all the highest types, the Cidaridte, Echinidi-e, Clypeastridie, Echinoneidte, Cassi- 

 dulida; and the Spatangida', Pryinnadete and Prymnodesmian, and there live, Avith rare 

 exceptions, the recent representatives of the fossil types of preceding geological periods. 

 But not one among the known living species, not a single fossil') among the multitu- 

 des imbedded in the sediments of former seas, had suggested the possibility of a 

 combination of characters like that realised in the Pourtalesiada3, and science was not 

 aware of its existence, until, a few years ago, dredge and trawl descended into the 

 vast regions of the great depths, where life endures on hard terms, far beyond the 



') Al. Agvssiz, ill the list of known recent species, Hep. Chall. Eciiinoidea, p. 208, doubtingly adduces 

 as possibly a Tertiary representative of the Pourtalesiadie, the fragment described by Edw. Forbes as 

 Echiiiarachniits Woodii, Echinodennata of the British Tertiaries, Palreontographical Society, 1852, p. 12, 

 pi. 11, fig. 6 a, 6 b. Professor V. Jui'frey Bell has had the kindness to examine for me the original 

 specimen of Forbes, now in the British Museum. There seems to be no reason whatever for regarding 

 it as having being part of something like a Pourtalesia. I arrived at the same conclusion from the in- 

 spection of another fragment, also from Crag, lent me by Mr Robert Bell, Chiswick. 



