INTEODUCTION TO THE MOLLUSCA. ix 



the main land, may possibly assist in determining a peculiar Fauna, but as we did not visit the 

 opposite shores of Asia, we were unable to judge from personal observation if such is the 

 case; near Botel Tobago sounding could not be obtained with 150 fathoms of line. The 

 Meiacoshima group, though never forming Attolls, abounds in barrier reefs and coral fringes, 

 which sometimes extend from a half to three-quarters of a mile from the shore. Fissurellcs 

 abound within the reefs, where the vegetation is abundant, and where, together with JEmar- 

 ginulcB, they crawl among the branches of the arborescent Alga. The fiats and plains 

 covered with coral, forming extensive shoals among these islands, are frequently dry at low 

 water, where Mitra exasperata and arenosa, with Turbo, Bicinula, Conus, Cyprcea, Lima, 

 Pecten, Terebra, Pteroceras, &c, occur in tolerable abundance. 



The superficial temperature gradually diminishes from the tropical seas towards the 

 southern hemisphere ; hence we find the forms of molluscous animals growing less numerous 

 and of less brilliancy of colouring as we recede from the equator. The most favourable 

 localities for harbouring Mollusca are among the bays and reefs of archipelagoes where 

 the coasts are low and shelving, and where the water remains shallow at some distance 

 from the shore. On this account the Philippine and Gallapagos Islands afford rich harvests 

 to the collector, but bold and rugged coasts, particularly if the result of volcanic agency, 

 are not prolific in mollusks ; the waves dash against them and rend off large masses, which, 

 falling into the sea, alter the nature of the floor, while the soundings give a great depth of 

 water close in shore. This we found to be the case with the Bashees ; when, however, the 

 tops of ancient submarine mountains are crowned with belts of coral, as in the Loo-Choo, 

 Meiacoshima, and Corean groups, mollusks are tolerably abundant-; but even here their 

 existence seems to depend upon the presence of coral. In Quelpart, for instance, where the 

 perpendicularity of the sides of this deep-seated submarine mountain will not allow of the 

 formation of coral, few shells are found. This island appears to be surrounded by a zone 

 of lower submerged hills, for in lat. 33° 24' N., 127° 47' E., we made the east point 

 (west 37") and obtained soundings in fifty-five fathoms ; as we neared the land, however, 

 the water gradually increased till within a distance of five miles, when it again gradually 

 decreased, and the same circumstance was observed on approaching it at other points. 

 Haliotis gigantea was found strewing the ground in large numbers ; the Terebratula picta 

 of Chemnitz, and other species, were obtained from the deep channels between the islands, 

 and Stomatia rubra and Crepidula from the reefs. 



