dall: mollusca and brachiopoda. 209 



that the separation between the abyssal fauna of the Pacific and that of 

 the Antilles is very ancient indeed, for in the sliallows many of these 

 groups are represented on both sides of the isthmus of Darien, yet have 

 not succeeded in reaching the deep water. That they can endure life 

 in the abysses and are not kept out by any physiological character- 

 istics which unfit tliem for life in deep water, is proved by the fact that 

 on one side or the other they do at present flourish there, thougli not on 

 both sides. 



The peculiarities of distribution, when analyzed, prove remarkably 

 interesting and not a little puzzling. 



For instance, tlie following Antdlean groups, some of which are very 

 populous in species, are not revealed in the Pacific dredgings from deep 

 water : 



Ovulactacon Aurinia 



Ringicula Turbonilla 



Trigonostoma Addisonia 



Benthobia Microgaza 



Conomitra Dillwjnclla 



Mitra " Basilissa 



Nassarina Pleurotomaria 



Daliuni Fissurisepta 



Eudolium Pectinodonta 



Triforis Lepetella 



Cerithiopsis Hanleyia 



Sella Limaea 



Matliilda Spondylus 



Fluxina Dimya 



Clathrella Astarte 



Rissoa Liocardium 



Benthonella Meiocardia 



Ilyalorisia Abra 



Olivella Euciroa 



Marginella Thecidium 



Voluta Megatliyris 



The above list includes the more conspicuous instances only. 

 On tiie other hand the Pacific fauna has the following groups not rejv 

 resented in tlie Antillean deep sea : 



Irenosyrini Surculina 



Steira.xis Narona 



Calliotectuin Adelomclon 



Rorsonolla Miomolon 



riiymorliynchus Tractolira 



VOL. XMII. — NO. 14 



