43 



Because of these adverse conditions, few benthic animals can live in these 

 lagoons permanently, and they are frequently barren of macro-invertebrate 

 life. Nichols (1962, 1963 and personal communication) has studied one of 

 these Sonoran lagoons (Laguna La Cruz) and states there was evidence 

 that oysters and mussels may have at one time been very abundant, but 

 are not living there now. Personal observations of Indian middens in the 

 vicinity of the same lagoon north of Guaymas revealed the existence of a 

 number of lagoonal or brackish-water mollusk species. These species may 

 have been living in the Sonoran lagoons during the supposed pluvial 

 period occurring about 900 to 1,000 years ago in the northern Gulf region 

 (HuBBS and Miller, 1948 and personal communication). 



The lagoons from Rio Fuerte south to Mazatlan are still situated in a 

 semi-arid climate but receive considerably more fresh water from the 

 rivers, which are more or less permanent. These lagoons permit the ex- 

 istence of seasonal populations of shrimp and permanent beds of oysters, 

 but little is known of the other inhabitants. It is known, for instance, 

 (Fred B Phleger, personal communication) that the salinities in this 

 group of lagoons may fluctuate widely, being almost fresh during the brief 

 rainy seasons, and hypersaline during the peak of the dry season. The 

 exact range of salinities is at present unknown to this author. 



A series of large lagoons south of Mazatlan to San Bias are very distinct 

 geologically (Curray, in van Andel in press) and hydrographically. They 

 are for the most part in the low salinity range, although the northern ones 

 may have high salinities in the summer. A permanent population of shrimp, 

 Corbula, oysters and Anadara clams live there, which are utilized for food. 

 These lagoons from the San Bias region to Manzanillo are true estuarine or 

 low-salinity lagoons, whose counterparts were studied along the humid por- 

 tion of the Texas-Louisiana coast (Parker, 1959). Rainfall and river dis- 

 charge are sufficient to maintain a permanent low salinity regime in at least 

 some portions of every lagoon. Unfortunately, no exact figures are available 

 to this author as to the range of physical factors, although they have been 

 studied in some detail by Fred B Phleger and Gifford Ewing (in 

 preparation). Personal collections of faunas from these lagoons were not 

 made, but a few forms were collected for the author by Joseph R. Curray 

 and Fred B Phleger. 



General Circulation within the Gulf of California. 



The circulation in the Gulf of California has been discussed by Roden 

 (1958, pp. 32-37), but a short discussion of the general characteristics must 

 be given here to supplement the survey of the general physical description 



