[19] INSTRUCTIONS FOR COLLECTING MOLLUSKS BALL. 



We are yet ignorant as to whetlier the abyssal and archibentlial 

 faunae shade gradually into one another, as seems most probable ; or 

 whether there is any line of depth, coincident with a temperature limit, 

 which really fixes a boundary ior the abyssal fauna. 



To give the student some idea of the kind and distribution of life in 

 the different benthal regions of the sea, two tables have been prepared 

 which illustrate the peculiarities of the collection made during the past 

 ten years on the southeastern shores of the United States and in the 

 Antilles by the United States steamer Blake and recently reijorted on. 



It is iDrobable that it offers a fair example of abyssal mollusk faunas, 

 but this can not be claimed with certainty. 



The first table shows the general numerical results for the Blake 

 collection, assorted among the great systematic groups and the three 

 bathyraetric zones or areas. The second table shows the proportion to 

 the whole population of the abyssal region borne by those genera which 

 exceed a single species. The result here shown is that less than 37 per 

 cent of the genera comprise more than 68 per cent of the species ; and 

 out of these, three families, Pleurotomidce, Ledidce^ Dentaliidw, furnish 

 nearly 28 per cent of the species of the abyssal fauna collected by the 

 Blake. 



Table I. — General numerical results. 



Groups. 



Brachiopods 

 Pelecypods . 

 Scapliopods. 

 Gastropoda - 



Total - 



No. of 



No. of 

 species, 



180 



13 

 170 



35 

 491 



Species iu the- ! ^P?^if^,i'l'^- | Abyssal fauna. 



Literal 

 area. 



709 



98 



17 



280 



Archi 



benthal 



area. 



12 

 114 



28 



A bvssal 

 area. 



Two 

 areas. 



All 

 areas. 



3 1 8 



31 i 64 



12 I 17 



83 j 161 



129 



250 



Fami- 

 lies. 



Genera. 









2 



2 



3 



10 



15 



19 



5 



1 



2 



32 



29 



41 



49 



47 



65 



Table II. — Genera represented by more than one species in the abyssal area. 



Genera. 



No. of 

 species. 



Mangilia 



Margarita 



Pleurotoma 



Drillia 



Marginella 



Scala 



Calliostoma 



Triforis 



Actffion 



Utriculus 



Fnsus 



Cokimbella 



Bentlionella 



Total, 24 genera and 87 species 



Genera. 



Flnxina . . . 



Liotia 



Leptothyra 

 Cocculina.. 



Leda 



Limopsis . . 



Pecten 



Abra 



Myonera. . . 



DentaliuiQ. 

 Cadulus . . . 



No. of 

 species. 



