8 



a period of years (Parker, 1955, 1956, 1959, 1960, and Parker and 

 CuRRAY, 1956), and were summarized in a volume by Shepard, etal. 

 (1960). 



The Gulf of Mexico provided one particular setting for depositional 

 environments, but because of its climate, geography and geologic setting, 

 did not include many of the modern counterparts of the ancient environ- 

 ments. For this, and other reasons, investigations were transferred to the 

 Gulf of California (fig. 1) in 1958, which in its climate, geology and geo- 

 graphy is a completely different type of region. Whereas the macro- 

 invertebrate investigations were concentrated in the lagoons, bays and 

 continental shelf of the Gulf of Mexico, the investigations of the Gulf 

 of California took place mostly in depths of 10 to 35 fathoms (18 to 64 

 meters) on the continental shelf, and to depths of over 2,000 fathoms 

 (4,000 m.) on the slope. Virtually no sampling was carried out in the 

 lagoons, bays and river mouths. The investigation of the Gulf of California 

 was also limited as to the number of stations occupied. Although nearly 

 2,000 biological samples were taken during the eight years of collecting 

 in the Gulf of Mexico, only 200 stations were occupied in the Gulf of Cali- 

 fornia. The present study cannot be considered more than a reconnais- 

 sance which gave an indication of the gross assemblages of deposition. 

 It will, however, give some idea of where detailed studies could be carried 

 out and provide a basis for a more comprehensive program. 



The term assemblage is used throughout this study, since both the 

 living organisms and the shells and tests of previously living animals 

 found in the same samples were also included in the analyses. Biological 

 communities are generally considered an interdependent assemblage of 

 living animals (and plants) which are geographically bound by the various 

 ecological factors within a biotope. Most animal communities are regarded 

 as more discrete aggregations of abundant organisms, which are suspected 

 to be more or less dependent upon each other. Because of the diversity of 

 life found in most of the Gulf of California environments and the variety 

 of gear (most of it non-quantitative) used, one had the feeling that each 

 sample might be considered a separate community. It was, therefore, more 

 convenient to designate assemblages, loosely bound together by a number 

 of species, which although possibly not abundant or dominant in the 

 quantitative sense, are found frequently enough throughout the biotope 

 to be considered indicative of the biotope. 



Not all of the stations occupied in this study were taken in the Gulf 

 of California proper, since portions of the program were carried out as a 

 study of the faunas of the continental slope. Those stations concerned 



