96 



Emerson, only 12 can be considered part of the rocky shore assemblage. 

 Two corals were also cited which are now living at Maria Cleophas Island 

 and Cape San Lucas. The rest of the fossil moUusks from Ceralvo Island 

 belong to the shallow, nearshore shelf environment, and as Emerson states, 

 it is a mixed fauna resulting from the reworking of the attached and non- 

 attached elements of that region. The Pleistocene fauna from Maria 

 Cleophas Island (Hertlein and Emerson, 1959) is primarily a level-bottom 

 fauna. Of the 28 species found at this locality, only eight were attaching 

 forms usually found on intertidally exposed rocks. This seems somewhat 

 surprising, since most of the present shoreline of Maria Cleophas is rocky, 

 and the surrounding shelf is very narrow, providing little level bottom for 

 the majority of these species which prefer this habitat. This very narrow 

 shelf was observed personally in a survey around the island in 1959 

 (FoosE, 1962). Few of the rocky shore animals cited in the present survey 

 are listed from the fossil deposits in northwestern Baja California, although 

 the majority of the fossils are rock-living species normally found on the 

 California coast (Emerson, 1956; Addicott and Emerson, 1959; and 

 Emerson and Addicott, 1958). A discussion of the fossil corals from the 

 Gulf of California, some of which were taken intertidally in the present 

 study, can be found in Squires (1959). 



II. Intertidal Sand Beach and Sand-Flats to 10 Meters: 



This assemblage is quite similar in composition throughout all warm- 

 temperate to tropical regions of the world where sand-flats and beaches 

 exist (Pearse, Humm and Wharton, 1942, Schuster, 1956, and Gauld 

 and Buchanan, 1956). For instance, a comparison of the surf-zone and 

 inner shelf, sand bottom assemblages of the northern Gulf of Mexico 

 (Parker, 1960, pp. 320-321) with its equivalent in the Gulf of California 

 reveals a great many similarities, especially at the subgeneric level of 

 mollusks and crustaceans. For nearly every species of moUusk, crustacean 

 and echinoderm listed for the Gulf of Mexico nearshore sand-bottoms, 

 there is an equivalent species in the same environment in the Gulf of 

 California. Many of the species from both Gulfs can be considered twin 

 species, with common ancestors in the Miocene and Pliocene of Panama 

 and Columbia (Olsson, 1961), which at that time was an open seaway 

 between the Caribbean Sea and the Pacific Ocean. This phenomenon has 

 been discussed at length for several invertebrate groups and fish by 

 Ekman (1953, pp. 30-38). The principal difference between the two regions 

 is that there were many more species in this environment in the Gulf of 

 California, even though sand beaches are the dominant feature of the coast 



