94 Subsurface Geologic Methods 



Supplementing the preceding data, information on other microfaunas 

 and microfloras, lithologies, and mineralogy is also recorded and has been 

 found to improve ecologic interpretations. 



OSTRACODES 



Next in importance to Foraminifera in economic micropaleontologic 

 analysis are the ostracodes (fig. 40) . These organisms, which are small, 

 bottom-dwelling, bivalved crustaceans range in length from 0.5 mm. to 

 2.0 mm. They thrive under variable conditions, marine, brackish, and 

 fresh water. The most diversified assemblages are those which inhabit 

 shallow-marine environments. W. T. Rothwell (Richfield Oil Corp., Cal- 

 ifornia), in his studies on the distribution of living ostracodes of Newport 

 Bay, California, show them to exist in the following salt-water environ- 

 ments: (1) tidal flat, (2) marsh channel, (3) lagoon channel, (4) bay- 

 mouth and subtidal channel, and (5) open-sea rocky-tide pool. He further 

 comments that the plants appear to be a major biologic factor influencing 

 the distribution of the ostracodes at this locale. Further investigations by 

 Rothwell of recent forms from samples across the San Pedro Channel 

 and from collections along the California coast, indicate that this group 

 of animals adjust to various water depths as do the Foraminifera. 



Ostracode carapaces (shells) in some sediments may constitute the 

 bulk of the material. Geologically ostracodes extend upward from the 

 Ordovician. Those of the Paleozoic assume carapace characteristics that 

 are pronouncedly different from those of the Mesozoic and Cenozoic. 



The external or surface pattern of the valves is extremely variable 

 and complex. Since most species molt (periodically shed their valves and 

 then form new ones), surface features are not constant throughout their 



EXPLANATION OF PLATE 4 



Figure 

 1- 4. Hemicy there? californiensis LeRoy var. hispida LeRoy X 29. Fig. 1, right 

 valve. Fig. 2, dorsal view. Fig. 3, ventral view. Fig. 4, interior view of 

 valve showing hinge structure. 

 5- 9. Bairdia verdesensis LeRoy X 24. Fig. 5, right valve. Fig. 6, dorsal view. Fig. 

 7, ventral view. Figs. 8, 9, inside view of left and right valves. 



10-13. Caudites fragilis LeRoy X 60. Fig. 10, right valve. Fig. 11, dorsal view. Fig. 

 12, ventral view. Fig. 13, inside view of right valve. 



14-18. Hemicythere palosensis LeRoy X 42. Fig. 14, right valve. Fig. 15, dorsal view. 

 Fig. 16, ventral view. Figs. 17, 18, interior views of right and left valves. 



19-23. Loxoconcha lenticulata LeRoy X 42. Fig. 20, dorsal view. Fig. 21, ventral 

 view. Figs. 22, 23, inside views of right and left valves. 



24-27. Cythereis kewl LeRoy X 37. Fig. 24, right valve. Fig. 25, dorsal view. Fig. 

 26, ventral view. Fig. 27, inside view of left valve. 



28-30. Cytheropteron minutum LeRoy X 37. Fig. 28, oblique view of right valve. Fig. 

 29, right valve. Fig. 30, posterior view. 



31-39. Characteristic muscle-scar patterns of left valves. Fig. 31, Hemicythere? 

 californiensis var. hispida. Fig. 32, Hemicythere? californiensis. Fig. 33, 

 Brachycythere lincolnensis. Fig. 34, Hemicythere palosensis. Fig. 35, Bas- 

 slerites delreyensis. Fig. 36, Brachycythere driveri. Fig. 37, Bairdia verdesen- 

 sis. Fig. 38, Paracypris pacificus. Fig. 39, Hemicythere jollaensis. 



