364 NORTH AMERICAN INDEX FOSSILS. 



1889. Dall, W. H. Bull. U. S. Nat. Mus. 37 (geologic distribution 

 of recent species of southeastern coast of North America). 



1893. Stanton, T. W. Bull. U. S. Geol. Surv. 106 (Colorado For- 

 mation). 



1893. Cragin, F. W. Fourth Ann. Rep. Geol. Surv. Tex. (Cretacic). 



1895-1903. Dall, W. H. Trans. Wagner Free Inst. Sci., vol. 3, parts 

 3-6 (Tertiary). This exceedingly valuable work revises the classifi- 

 cation of the pelecypoda and gives a critical discussion of most of the 

 later genera and many species. It is indispensable to the student of 

 Pelecypoda. 



1895 to date. Inst. Geol. Mexico Boletin. 



1895. Stanton, T. W. Bull. U. S. Geol. Surv. 133 (Knoxville of 

 California). 



1896-1897. Harris, G. D. Bull. Am. Pal. 4, 9 (Eocenic [Midwayan 

 and Lignitic] of Gulf region). 



1897. Ulrich, E. 0. Geol. Surv. Minn. 3, part 2. (A most impor- 

 tant discussion of the Ordovicic pelecypods throughout the middle 

 west. Especially good for generic descriptions.) 



1898. Hill and Vaughan. Bull. U. S. Geol. Surv. 151 (Lower Cre- 

 tacic Gryphaeas of the Texas region). 



1900. Beede, J. W. Univ. Geol. Surv. Kansas 6, part 2 (Carbonic). 

 1903. Clarke, J. M. Naples Fauna. Mem. 6, N. Y. State Mus. 

 1901-1906. Clark, Martin, Glenn. Md. Geol. Surv. (Eocenic- 



Pleistocenic). 

 1906. Arnold, Ralph. Prof, paper U. S. Geol. Surv. 47 (Cenozoic 



Pectens of California) . 



(See also references under Faunal summary.) 



Artificial Key to the Genera. 



A. Distinct hinge-plate absent; also hinge margin usually thin and without teeth ; 

 when teeth are present they are merely modifications of the hinge margin and 



not set upon a hinge plate.. Two subequal adductor scars I. 



I. Pallial sinus absent ; also pallial line usually obscure. Almost confined to the 



Palaeozoic I . 



I . Beaks very anterior a. 



a. Shell transversely elongate ; hinge and basal margins subparallel II. 



11. Shell moderately elongate; umbonal ridge slight aa. 



aa. Anterior end vertically subtruncate from edge of beak. 



VII. Cuneamya. 



aa. Anterior end projecting forward from beak |. 



■f. Beaks very prominent and incurved *. 



*. Hinge margin thin XV. Cardijmorpha. 



*. Hinge margin thickened X. Grammysia. 



f. Beaks not prominent **. 



**. A broad sinus present basally anterior to umbonal ridge. / 7/ . 



