Clark: The San Lorenzo Series of Middle California 161 



latter the hinge plate is heavier, the resilium pit is larger and not so 

 deep and well-defined ; also there is only one well-defined ridge 

 posterior to resilium pit and it does not extend out beyond the edge 

 of platform of chondrophore as on M. incognita. 



M. incognita somewhat resembles in outline Mya (Cryptomya) 

 oregonensis Dall, 133 from which it differs in being more obliquely and 

 strongly truncated; the two valves of M. incognita are equal, while 

 Dall describes M. oregonensis as being "moderately unequivalve." 



Family Saxicavidae 



Genus PANOPE Menard 



PANOPE ef. ESTEELLANA Conrad 



Glycimeris estreUana Conrad, Pacific Railroad Rep., vol. 7, p. 194, pi. 7, 

 fig. 5, 1857. 



Panopea estreUana Conrad, Smith, Proc. Calif. Acad. Sei., ser. 4, vol. 3, 

 p. 173, 1912. 



Panope estreUana Conrad, Anderson and Martin, Proc. Calif. Acad. Sci., 



ser. 4, vol. 4, p. 42, 1914. 

 Panope estreUana Conrad, Clark, Univ. Calif. Publ., Bull. Dept. Geol., 



vol. 9, no. 2, p. 15, 1915. 



The type of Panope estreUana came from the southern part of the 

 state. It is not known for a certainty whether it came from the Lower 

 or Upper Miocene of that region. The Recent species, P. generosa 

 Gould, 134 is rather variable in outline and sculpturing ; this is also true 

 of the form found in the Lower Miocene and Oligocene, referred to 

 here as P. estreUana. Some authors have concluded that the variations 

 of the Recent and Oligocene-Lower Miocene forms are so great that 

 they can not be separated as distinct species. After examining a 

 considerable number of specimens from the Lower Miocene and the 

 Oligocene and of the Recent, the writer believes that the Oligocene- 

 Lower Miocene form is distinct ; he does not feel certain, however, 

 that the form described as Mya abrupta by Conrad and placed as a 

 synonym of Panope estreUana by Dall is not a distinct species. Pos- 

 sibly when good hinge plates are exposed of specimens from both 

 the Oligocene and Miocene, specific differences will be found between 

 them. 



133 For original description of Mya oregonensis see IT. S. Geol. Surv., Prof, 

 paper no. 59, pp. 132-133, pi. 11, fig. 4, 1909. 



134 For original description of Panope generosa, see Proc. Bost. Soc. Nat. 

 Hist., vol. 3, p. 215, 1850; for good redescription and discussion see Arnold, Mem. 

 Calif. Acad. Sei., vol. 3, p. 182, 1903. 



