358 report — 1856. 



quil, each portion (the upper Gulf, the Gulf mouth, S. W. Mexico, Central 

 America proper, the Bay of Panama, the N. W. shores of South America, and 

 the Galapagos,) has its peculiar species, or at least those which culminate 

 in that locality. A large number, especially those which are also common 

 to the Galapagos, are found on the whole length of coast, wherever there is 

 a suitable station ; while others, perhaps nearly related species, are very local. 

 Thus the beautiful Venus gnidia is found wherever there is a muddy bottom to 

 protect its delicate frills, (Hi?ids); while the V.amathusia, so near that by Gray 

 and even Deshayes it is regarded as identical, has only yet been found in a 

 typical state at Mazatlan, straggling and of modified form below. The Dione 

 lupinaria is in extreme profusion at Mazatlan, and also found far down the 

 coast of South America ; but the D. brevispinosa, which resembles it with 

 blunted spines, has not yet come to light except from the Gulf. But we 

 must check these comparisons, so interesting to those who have made them 

 a matter of study ; and which, if developed, even according to our present 

 knowledge, would fill a volume. Nor would a history of even the Atlantic 

 waters, furnish materials for one more interesting and instructive. 



81. One fact however is deserving of special notice. On comparing the 

 shells of the Gulf and South America, we obtain the following results : — 

 Out of 143 Gulf Bivalves, 50 are found in South America, or 1 out of 2*86. 

 Out of 4-90 Gulf Univalves, only 89 have been found in South America, or 

 1 out of 5*5; while of the 151 Gulf Proboscideans, only 14 are yet known 

 from South America, or 1 out of 10*8. This may be accounted for partly by 

 the fact that the bivalves cast their spawn loose into the sea, while the uni- 

 valves, which have larger locomotive powers, generally affix their eggs to 

 shells and stones. ( Gray.) Accordingly, the Lamellibranchiate fry are borne 

 on in the direction of the current, and tire found far beyond what may fairly 

 be considered the limits of the species. This further accounts for the absence 

 of some South American bivalves from Panama which are however found at 

 Mazatlan ; the fry, with the current, not sweeping into the bay, but landing 

 on the Mexican coast. It is confirmed by finding the young of many South 

 American species in the sand of Mazatlan, which are not known there in 

 the adult state. Only two bivalves are quoted from Mazatlan and the Gala- 

 pagos (one of these, Modiola capax, a Gulf and Californian species, having 

 probably been added in error from Kellett's voyage) ; that group being out 

 of the current which we may suppose to convey species from Guayaquil to 

 the northern shores. 



How far the Gulf species, or those of Panama, extend on the South American 

 coast, we are not yet able to state with any confidence. Most of Mr. Cuming's 

 recorded South American species are from Ecuador and Columbia ; and 

 D'Orbigny's collections are too scanty, especially in pelagic species, for much 

 comparison. It seems probable that but few reach Callao, and extremely 

 few the coasts of Chili. A few indeed are quoted as far south as the Island 

 of Chiloe, but (except in the widely distributed forms, such as Calyptraeidae) 

 they need confirmation ; as do also the appearance of Crepidula nivea (Les- 

 sonii) and Lyonsia picta, both southern forms, at Vancouver's Island. 



82. A comparison with the shells of the Galapagos Islands offers points of 

 peculiar interest. They are known to us by the researches of iMessrs* Cuming 

 and Darwin, the latter of whom has given a most graphic picture of their 

 peculiarities in his 'Journal of Researches,' pp. 145, I6 l 2. Collections have 

 also been made there by Messrs. Kellett and Wood ; but for reasons before 

 stated, less dependence should be placed on them. Unfortunately, though 



