210 BULLETIN : MUSEUxM OF COMPARATIVE ZOOLOGY. 



Solenosteira Pallium 



Truncaria Acesta 



Tritonoliarpa Archivesica 



Capulus Pholadidea 



Clanculus Dermatomya 



Zeidora Hemithyris 



Spinula Terebratella 



Malletia (s. s.) Magellania 



Neilo Basiliola 1 



Even in the groups common to both regions there are some interesting 

 differences. 



Mangilia is numerous in the Atlantic, rather sparse in the Pacific ; 

 Fusinus rare in the Pacific, numerous in the Atlantic. Anachis, Murex, 

 Scala, Calliostoraa, Deutalium, Cadulus, Propreamusium, Phacoides, and 

 Venericardia are relatively common on the east and sparse on the west 

 of the continent. The total absence of the Triphoridae, Cerithiopsidae, 

 and all the group of Marginellidae from the fauna of the west is aston- 

 ishing, and incomprehensible with our present knowledge. Why sliould 

 Vesicomya on the east be moderate or small in size, and on the west 

 large even to gigantic ? 



Wiiy are there no Pyraraidellidae of any sort in deep water on the 

 Pacific side 1 Why should European or Japanese types of Pecten, Lima, 

 etc., appear on the west coast and be absent from the Antilles 1 These 

 questions will doubtless be answered in the future, but with our present 

 knowledge we can make no satisfactory reply. 



After a general survey and comparison of the two faunas, Atlantic and 

 Pacific, as developed by the " Albatross " and other dredgings, it may be 

 concluded thut the deep-sea fauna of the eastern Pacific is composed of 

 several elements. We have first a comparatively limited number of 

 abyssal forms of wide distribution. These are doubtless the descendants 

 of very ancient migrants to the deeps, and their precise number and 

 character can only be definitely known after much more extended ex- 

 ploration of the floor of the deep sea. Still, from our present knowledge, 

 it is practically certain that there is such a group of species, although 

 we cannnt as yet state how many of them there are. 



Secondly, there is a considerable number of species characteristic of 

 the Antarctic and Magellanic regions. Whether they are descended from 

 the present shoal-water fauna to which they are systematically akin, 

 mombers of which may have strayed into deeper water from time to 

 time and become acclimated there, or whether the deep-sea fauna and 

 tlio littoral fauna are both descendants of an Antarctic fauna which 



