ECHINOIDEA. II. 



187 



not have been overlooked in the regions, from where they are hitherto not recorded. It seenis tlien 

 really to be the case, that also the Atlantic deep sea comprises several distinct regions, though it seems 

 impossible for the present to point ont special physical characters, which distinguisli the separate re- 

 gions. As seen in Gerh. Schott's admirable vOceanographie nnd maritime Meteorologie»' the bottom 

 temperature is in the whole Atlantic, in depths beyond 1000 M., over 2°. Only in the Davis Strait 

 and in the large Brazilian basin to the West of the midatlantic ridge (from near St. Paul down to the 

 antarctic sea) the temperature is below 2°. But this difference in the temperature does not seem to 

 be sufficient to cause corresponding marked differences in the deep-sea Echinoid-fauna. 



The subdivision of the deep-sea regions into an archibenthal and abyssal zone is upon the whole 

 not supported by the bathymetrical distribution of the species; most of the species occurring in the 

 abyssal zone also occur in the archibenthal zone, and probably several of the species hitherto not 

 known beyond the archibenthal zone will ultimately prove to have a greater bathymetrical distribution. 

 Still it is wortli noticing that the Meridosternata almost exclusively belong to the abyssal zone. 



The European Atlantic deep-sea region comprises the Northern Atlantic, to the E^ast of a 

 line from the Denmark Strait to the Gibraltar Strait.^ It is limited from the cold area of the Nor- 

 wegian Sea by the ridges across the Denmark-Strait, the Faroe-Channel and between Iceland and the 

 Faroe Islands. 



The following species are known from this region : 



Trigonocidaris albida 

 Hypsiechinus coronatus 

 Echinus esculentus 

 — acutus 



Dorocidaris papillata 

 Stereocidaris ingolfiana 

 Porocidaris purpurata 

 Phormosonia placenta 

 Calveria hystrix 

 Aræosoma tenestratum 



— violaceum 



Hygrosoma Petersi 

 Sperosoma Grimaldi 

 Echinosoma uranus 

 Salenia hastigera 



elegans 



Urechinus naresianus 

 Plexechinus hirsutus 

 Pourtalesia Wandeli 

 Echinosigra (Pourtalesia) phiale 



— — paradoxa 



Hemiaster ex^iergitus 

 Brisaster fragilis 



— Alexandri 

 affiuis 



Strongylocentrotus drobachiensis Spatangus purpureus 

 Sphærechinus granularis — Raschi 



Echinocyamus pusillus Echinocardiuni flavescens 



Neolamj^as rostellata Brissopsis lyrifera. 



Of these species we raay first eliminate the following as occasioual intruders from the boreal 

 and Mediterranean regions: Echinus esculentus, Strongylocentrotus drobachiensis, Sphærechinus granu- 

 laris and Echinocardium flavescens. Of the rest the following are known from this region only: Aræ- 

 osoma violaceum, Echinosoma tiraiius, Hypsiechinus coronatus, Plexechinus hirsutus, Echinosigra (Pour- 

 talesia) phiale and paradoxa. Porocidaris pnrpnrata and Sperosoma Griiitaldi are known only from this 

 and the West African region. These si^ecies are, however, (except Porocidaris ptirpurata and Spero- 

 soma Grimaldi) either small or easily confused with other .species. It is certainly not much to 

 characterize the region by, but especially Porocidaris purpurata and Sperosoma Grimaldi are so mag- 

 nificent and peculiar forms that they eau certainly not have been confused with other species; the 



1 Wissensch. Ergebn. d. deutsch. Tiefsee-Exp. I. 1902. 



2 The limit between the European and the East American Atlantic deep-sea regions will undoubtedly prove not to 

 be a straight line of the course here indicated. For the present, however, our knowledge of the deep-sea faitna of the Mid- 

 Atlantic is too insufficient for pointing out the limit between these regions more exactly. 



24* 



