362 report— 1856. 



quoted from the continent ; two [?] from the Gulf; one from Panama ; the 

 other (a distinct variety), from deep water, from Isle Plata. On glancing 

 over the genera with their stations, it will be found that the coast shells 

 common to the two are more numerous than those from deep water ; and 

 that the general aspect of the collection is essentially American*. The only 

 genus not yet found on the coast is Stylifer, which may indeed afterwards 

 receive species now placed in kindred genera, or be discovered on due search 

 of Echinoderms. 



83. Scarcely any generic forms are peculiar to the West Coast Fauna ; except 

 indeed Platyodon, Cryptodon and Mytilimeria, from California ; Leiosolenus, 

 from the Gulf; Callopoma and Tei?iostoma, from the Central Province, and 

 Concholepas from Peru. But many attain here their greatest development; 

 especially Calyptrceidce, Fissurellidce, Acmcea, Uvanilla, Pomaulax, Ccecum, 

 Chrysallida, Monoceros, Leucozonia, Cancellaria, Columbellidce, Periploma, 

 Parapholas, Saxidomus, Trigona, &c. The familiar genera of the East are 

 often entirely absent ; especially the shell-bearing Cephalopods, Stomatellidce, 

 Dolium, Melo,Ebuma,Ancillaria, Rostellaria, Pterosceras, Phorus, Placana, 

 Malleus, Tridacnidce, Glauconome, Meroe, Anatina, Aspergillum, &c. Others, 

 abundant in the Indo-Pacific province, are here barely represented by a few 

 species, or by minute or aberrant forms. Such are Marginella, Cithara, 

 Liotia, Rimula, Cypricardia, dementia, Circe, Mesodesma, Crassatella, 

 Pythina and Scintilla ; and the tribes of Cassidce, Harpidce and Volutidce. 

 The genera Conus, Oliva, Cyprcea, Terebra, &c, the staple commodities of 

 the East, are here but poorly represented ; no large Cowry living on the 

 coast except Cyprcea exanthema, and not a single species having been yet 

 found in South America below the Bay of Guayaquil. {Hinds.) The almost 

 entire absence of coral, so common in the West Indies and Polynesia, is to be 

 remembered in connexion with the paucity of those tribes that usually feed 

 on its banks. 



84. The point, however, which may prove most interesting to the geologist 

 and the geographical student, is whether there be any species common to the 

 Pacific and the Atlantic shores of tropical America ; and if so, what are they ? 

 It is easy for man to cross the narrow isthmus; have any Mollusks done the 

 same? The determination of this question is a matter of great difficulty; 

 for while ordinary naturalists treat shells as of the same species, if there be 

 no greater variation between them than is known to be allowable between 

 individuals under the same name, it is the present custom with geographical 

 conchologists to treat all similar shells as " analogues " or " representative 

 species," if they occur in unexpected places. In arranging the materials of 

 this Report, those species have been treated as absolutely identical, 

 where no difference obtained between the shells of different seas greater 

 than was observed between individuals in one sea. Thus when the supposed 

 peculiarities of the Pacific Purpura pansa, Gld., and Trochus picoides, Gid. 

 are found in West Indian specimens, it is regarded as a mere deference to 

 theory to keep them distinct. In other cases, where the shells of the two 

 coasts have a marked difference of aspect, though not greater than may 

 obtain in the same species, if a separation has been made, it is temporarily 

 allowed, though it is more than probable that they will hereafter prove 

 identical. In other cases, the differences, though slight, appear permanent 

 and specific; and in a fourth group they are simply "interesting analogues," 

 but would at once be pronounced distinct, although from the same shore. 



* Dr. Gray states [Dr. Richardson's Rep. Ichth. Chin, and Jap. 1846, p. 191, note] that the 

 reptiles which inhabit the Galapagos also belong to American groups. 





