Xliv PKOCEEDINGS OP THE GEOLOGICAL SOCIETT. 



Besides giving the lists and range in depth of the Mollusca and 

 Radiata, the Report entered into the question of their distribution 

 considered in its bearing on geology. The observations of Prof. 

 Porbes ranged over a period of eighteen months ; and his lists are 

 based on more than 100 fully recorded dredging-operations in va- 

 rious depths from 600 to 780 ft., besides numerous coast-observa- 

 tions. The result of this valuable and special inquiry was to de- 

 termine more clearly than had hitherto been done the range of species 

 in depth, and the division into zones first proposed by Risso. With 

 regard to much that Prof. Forbes accomplished no question has 

 arisen. Of the eight zones into which he divides the bathymetrical 

 distribution of the Mollusca, the first seven, ranging from the surface 

 to the depth of 630 ft., although possibly too much subdivided, may be 

 applicable to other seas where the conditions are similar ; but with 

 respect to his eighth region, Avhich extends from 630 to 1380 ft.. 

 Prof. Porbes's generalizations, although correct within certain areas, 

 have been found inapplicable to the two great oceans and applicable 

 only to parts of the Mediterranean. He observes, speaking of this 

 eighth zone, ''throughout this great and, I may say, hitherto unknown 

 province, we find an uniform and well-characterized fauna ;" but 

 then he goes on to say, " within itself the number of species and of 

 individuals diminishes as we descend, pointing to a zero in the 

 distribution of animal life as yet unvisited." He placed this zero at 

 about 1800 ft. 



In a subsequent work *, however, in speaking of the eighth re- 

 gion of depth, E. Forbes remarks, " its confines are yet unde- 

 termined, and it is in the exploration of this vast deep-sea region 

 that the finest field for submarine discovery yet remains." " In 

 the Mediterranean, as might be expected, when we consider the pe- 

 culiar condition under which that great land-locked basin is placed, 

 there are peculiarities in the distribution of both animal and vege- 

 table life which require special consideration ;" and in speaking of 

 animal life in the " Arctic province " of the Atlantic, he notices 

 that the MoUusca appear to range much deeper in high latitudes 

 than they do in more favourable climates, and mentions the ca- 

 pital haul made by Mr. Harry Goodsir in Davis's Straits, when 

 a variety of shells, Crustacea, Echinoderms, and Corallines were 

 brought up from a depth of 1800 ft. 



In another Report f, on British Marine Zoology, E. Forbes di- 

 vided the range of the MpUusca into only four zones of depth ; and 



* Natural History of European Seas, p. 27. t Brit. Assoc. Rep. 1850. 



