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I28l 



TERTIARY FAUNA OF FLORIDA 



ternary of California as well as living on the coast from Baulinas Bay to San 

 Diego. 



Saxidomus giganteus of Deshayes (as Venerupis, 1839), the S. Nuttallii 

 of Carpenter, 1864, but not of Conrad, the 6\ squalidus of Carpenter but not 

 of Deshayes, 1853, is the common species of Alaska and Northern California, 

 and is said by Cooper to occur in the Pliocene and Quarternary of Southern 

 California. 



Saxidomus gibbosus Gabb, 1866, from the Miocene of Coos Bay, Oregon, 

 and Humboldt County, California, is probably a species of Marcia closely re- 

 lated to M. subdiaphana Carpenter of the recent fauna of the coast. 



Saxidomus Petitii Deshayes is identical with a variety of Paphia (Proto- 

 thaca) staminea Conrad, 1837, which is abundant from the Miocene up in the 

 Tertiary of California and living on the coast. 



Subfamily VENERIN^E. 



There does not seem, a priori, any very good reason why the presence or 

 absence of a minute pustule of shelly matter in front of the cardinal teeth 

 should count for much in the classification of species, genera, or still less be 

 the criterion for determination of the subfamily to which a species belongs. 

 Yet in making comparisons of the anatomical features of these animals this 

 little tooth or pustule is found an excellent index to important anatomical 

 differences. So whether it has any intrinsic value or not its correlation with 

 important characters for systematic use must be admitted. 



The differences indicated already appear with the early Venerida in the 

 Mesozoic. The lines of development have been varied. On the one hand we 

 note faint granulation or corrugation near or on the posterior cardinals, grad- 

 ually either splitting up the existing teeth or inducing the establishment * of 

 entirely new ones, as in Tivela. On another line the teeth descend from thin 

 ancestral Mesozoic progenitors (Baroda) to the present representatives of the 

 earlier forms (Tapes) with hardly a trace of modification. 



Anyone who studies these peculiarities must frequently wonder if the key 

 to all of them will ever be attained, and acknowledge with humility the limita- 

 tions of our present knowledge. 



The present subfamily is characterized by the total absence of lateral teeth. 

 The siphons are usually comparatively short and more or less separate from 

 each other. The foot is hatchet-shaped and, in the adult, not byssiferous except 

 among the nestlers. The young undergo their development outside of the 

 parent shell. 



