i86 



ECHINOIDEA. II. 



Agassizia excentrica Moira atropos Metalia pectoralis 



Periaster limicola Macropneustes spatangoides Meoma ventricosa 



Brisaster fragilis Echinocardiuni cordatuni Brissopsis elongata 



Schizaster orbignyanns Brissns nnicolor — atlantica. 



A considerable part (31) of these species exclusively belongs to this region, not occnrring else- 

 where, viz. 



Dorocidaris abyssicola 

 Tretocidaris Bartletti 

 Aspidodiadema Jacobyi 

 Arbacia punctulata 

 Echinus gracilis 

 Paracentrotus Gaimardi 

 Psammechinns variegatus 

 Echinometra viridis 

 Clypeaster latissimus 

 — Ravenellii 



Echinanthus rosacens 



Mellita sexforis 



— testudinata 

 Encope marginata 



— Michelini 

 Echinoneus semilunaris 

 Echinolampas depressa 

 Conolainpas Sigsbei 

 Rhyncopygus caribbæaruni 

 Palæotropus Josephinæ 

 Palæopneustes cristatns 



Palæopneustes hystrix 

 Linopnenstes longispinns 

 Palæobrissus Hilgardi 

 Agassizia excentrica 

 Periaster limicola 

 Schizaster orbignyanns 

 Moira atropos 



Macropneustes spatangoides 

 Metalia pectoralis 

 Brissopsis elongata 



Several of these species also occnr in the deeper regions, the limit between the littoral and 

 archibenthal zones being here especially arbitrary and not expressed in the bathymetrical distribution 

 of the species. 



Besides the above named 31 species the foUowing are also really characteristic of the region, 

 but have crossed the Atlantic, thus occnrring in the Mediterranean or West African tropical region: 

 Cidaris tribuloides, Diadema autillarum, Tripnciistcs esculentus, Echinometra lucunter,^ Clypeaster suå- 

 depressus and Meoma ventricosa. Two species, viz. Salenia Pattcrsoni and Coelopleurus floridamis also 

 occur at South Africa; it is scarcely possible to say, where their original home is. 



Among the rest of the species occnrring in this region one, Arbacia pustulosa, is an intruder 

 , from the Mediterranean region, while the remaining are either widely distributed over the Northern 

 Atlantic, viz. Dorocidaris papillata, Brisaster fragilis, or at least common to two or more regions, viz. 

 Cidaris affinis, Trigonocidaris albida, Genocidaris maculata, Ecliinocardiitm cordatuni, Brissns nnicolor 

 and Brissopsis atlantica Q). Forj the present, at least,| it is impossible to say whether these belong 

 originally to one or the other of the regions. 



The Atlantic deep-sea regions. Though the physical conditions of the deeper regions appear 

 to be of a very uniform character over the whole Atlantic, it is evident that the Echinoids occnrring in 

 the deeper regions are not all uniformly distributed over the whole Atlantic within the limits of their 

 bathymetrical distribution. Some species appear to occur exclusively at the European side of the At- 

 lantic, others only at the American side, while others still are known only from the Southern part of 

 the Atlantic. It seems therefore necessary to distinguish three Atlantic deep-sea regions, viz. the 

 European, the East American and West African. Undoubtedly several of the species hitherto known 

 from only one of these regions will prove to be more widely distributed, but on the other hånd several 

 of the species are so well known and characteristic that it may be regarded as certain that they can- 



I A very nearly related species, Echinometra pyisca, is described by Cotteau from the Miocene of Anguilla. (De- 

 scription des Écliiuides tertiaires des Iles St. Barthélemy et Anguilla. Sv. Vet. Akad. Handl. XIII. 1S75.) 



