160 REPORT — 1856. 



2. Perhaps no region in the world is so well adapted for the study of the 

 geographical distribution of Mollusca as the W. coast of N. and S. America. 

 Shut out from the vast Indo- Pacific province which reaches to the Sandwich 

 and Marquesas Islands by an uninterrupted body of water almost equal in 

 extent to the whole Atlantic Ocean, on the other side barred against all 

 admixture with the Caribbean Sea by the mighty bulwark of Central Ame- 

 rica and Darien, it presents the least indented line of coast that the world 

 can show, from the frozen ocean of the north to a southern promontory 20° 

 south of the lowest extremity of the old world. Even the land fauna is sepa- 

 rated from that of the bulk of the continent by the great chain of the Andes 

 and the Rocky Mountains, and by the arid climate which prevails over a 

 large portion of its extent. Here then we enter upon a new type of marine 

 life, almost entirely distinct from those with which we have been familiar in 

 the Atlantic, Indian and Polynesian waters ; in which we can pass, on each 

 side of the equator, from tropical to boreal conditions, with the most satis- 

 factory regularity. All that we miss is the presence of more oceanic islands ; 

 the solitary group of the Galapagos presenting data of unusual interest, to 

 be noticed afterwards. 



3. The tropical region of marine life extends much further north than 

 south of the equator. This is accounted for by the direction of the equato- 

 rial current, which, striking upon the swelling coast of Peru, sweeps round 

 the great Bay of Panama and Central America, and following the north- 

 westerly direction of the coast, is naturally driven up the narrow Gulf of 

 California, where, even at Guaymas, in lat. 27°, are found the conditions of 

 equatorial climate ( Gould). The long promontory of Lower California, from 

 lat. 23°-32°, offers a natural impediment to the further northward passage 

 of mollusks ; while the current which flows southwards, parallel to the 

 shores of temperate America, seems to convey many boreal species below 

 the latitude at which we should have expected them. The zoological tem- 

 perate zone therefore is curtailed in the northern and extended in the 

 southern hemisphere. 



4. The following are recorded as the physical conditions of places which 

 have been made the special seats of observation. — Panama. At the head 

 of an extensive bay, with a reef consisting of " ledges of trachytic rocks, 

 with flat and concave surfaces, and gently sloping, precipitous, or shelving 

 sides." Each has its appropriate species, as have also the loose pieces of 

 rock, according to their size, distance from each other, and amount of inser- 

 tion in the sand. On the fine sand beaches, Oliva, Tellina, Donax and 

 Dosinia abound. On trees a little above half-tide level are found Pur- 

 pura and Littorince ; with numerous Veneridcs, Columbe/lce, Neritina picla 

 and Area grandis among the sticks and moss-like algae beneath. On ledges 

 of smooth basaltic rocks abound Littorince, Fissurellce, and Siphonarice. In 

 a mangrove thicket at high-water mark occur Cerithidece, Cyrena, Arcce, 

 Potamomyce, Melampi, and " over head, Littorina pulchra, almost as rare as 

 beautiful." The ordinary tides are 16-20 feet, very rarely 28 feet, leaving 

 many square miles of sea-bed exposed at the ebb. The bay contains several 



and unrestricted use of his unrivalled collections, and the benefit of his experience and judg- 

 ment ; to Dr. A. A. Gould, of Boston, U. S., for the transmission of the whole of his valuable 

 materials, including lists and collections ; to R. M'Andrew, Esq., F.R.S., for the use of his 

 collections and library ; to R. D. Darbishire, Esq., B.A., of Manchester, and Sylvanus Han- 

 ley, Esq., B.A., for aid in the identification of species ; to Dr. J. E. Gray, Dr. Baird, and 

 S. P. Woodward, Esq., of the British Museum, for their assistance throughout ; to Prof. Dr. 

 Dunker for special help in the Mytilidae, W. Clark, Esq., in the Caecidae, and L. Reeve, Esq., 

 in the Patellidae ; and generally to friends and naturalists who have freely contributed mate- 

 rials at their disposal. 



