97 



of the Gulf of Mexico and constitute less than half of the shoreline of the 

 Gulf of California. The great variation in the size and sorting of sand 

 particles along the coast of the Gulf of California, as compared to only 

 very fine, well-sorted sands which are found along the northern Gulf of 

 Mexico coast, may account for the greater diversity of animals in this 

 environment in the Gulf of California. A greater range of water temper- 

 ature (0° to + 40° C.) in the northern Gulf of Mexico, as opposed to only 

 15° to 30° C. in the Gulf of California may offer an even better explanation 

 for lower species diversity in the Gulf of Mexico. 



Buchanan (1958) and Bassindale (1961) investigated the inshore 

 sand-bottom community in the tropics off Accra, Ghana, which is in the 

 same temperature province as the Gulf of California. Buchanan reports 

 two species of Donax, one of Tivela, a Bulla, a Terebra and an Olivella 

 from the surf zone, the same genera which are common to the surf zone 

 from somewhat deeper water in 6 to 15 meters on fine sand, which also 

 contains the same components as the inshore sand bottom community in 

 the Gulf of California. A complete list of these sand beach and sand flat 

 species of invertebrates off Ghana can be found in Buchanan (1958, 

 pp. 19-21) and Bassindale (1961, pp. 500-507). Longhurst (1958) in 

 his study of bottom communities off Sierra Leone, just north of Bucha- 

 nan's region, designated the shallow, nearshore sand-flat assemblage as 

 the Tellina iso-community. The dominant animals of Longhurst's Tellina 

 iso-community are Donax (= Tellina), Terebra, and a suspension feeding 

 polychaete, Spio, sp. The less abundant members are a polychaete (Siga- 

 lion), an amphipod (Urothoe), a Hippid crab {Albunea) and another species 

 of the gastropod, Terebra. 



One region of nearshore sea bottom in the tropics which seems to be 

 quite different from those discussed previously is located on the Malabar 

 coast of India. Seshappa (1953) collected a number of grab samples in 

 this region in depths to about 10 meters. The bottom temperature range 

 was from 26° to 30° C. (similar to that off Mazatlan), but because of the 

 Monsoons, salinities fluctuated widely from season to season (16°/oo to 

 35''/po). Seshappa's nearshore sand community bore little resemblance to 

 either its counterpart in the Gulf of California or those studied off West 

 Africa. A polychaete, Prionospio, was the only dominant, and Lucina 

 was the only genus of nine molluscan genera found there that was also 

 represented in an equivalent environment in the Gulf of California. 



It is impossible to obtain a quantitative conception of this assemblage 

 in the Gulf of California, since so many of the shallower samples from the 

 surf zone were taken by hand collecting. It was observed, however, that 



7 Vidensk. Medd. fra Dansk naturh. Foren. Bd. 126. 



