94 Trans. Acad. Sci. of St. Louis. 



from the types. The specimen which he separated from 

 E. burlingtonensis and described under the specific name 

 ellipsis should not be so separated. E. ellipsis therefore be- 

 comes a synonym of E. burlingtonensis. Some of the varia- 

 tions of E. subovata H. from the Chemung in New York and 

 Pennsylvania, approach very close to the Burlington species. 

 In fact, in his earlier publications,* Hall identified this Che- 

 mung species as E. burlingtonensis, it being separated only 

 in the final publication of the New York Paleontology. The 

 Chemung species exhibits a greater variation than the Burling- 

 ton species and for this reason it may perhaps be considered 

 as distinct, but some of its variations f are certainly identical 

 with the shell from Burlington. 



Edmondia quadrat a (W. &W.). 



PL IV. f. 1 7. 



Microdon quadratus. Bull. U. S. G. S. No. 153: 353. 



Shell small, subquadrangular in general form, length 12 mm., 

 height 9^ mm., thickness of the two valves 7 mm., greatest 

 convexity of the valve posterior to the beaks along the 

 umbonal ridge. Hinge-line slightly arcuate, gradually slop- 

 ing to the posterior margin ; anterior and posterior margins 

 subparallel; ventral margin greatly rounded. Beaks small, 

 slightly incurved; umbonal ridge obscurely angular, gently 

 arcuate. Surface marked bv fine concentric lines of growth 

 and by a few coarser concentric wrinkles. 



Remarks. When this species was originally described it 

 was referred to the genus (Jypricardella. More recently it 

 has been shown by Whitfield X that the genus Cypricardella 

 is not distinct from Microdon and for that reason this species 

 has sometimes been referred to the latter genus. Upon com- 

 parison of the type specimens of the species with authentic 

 specimens of Microdon, however, it is believed that it is more 

 probably an Edmondia although the essential generic char- 

 acters cannot be seen. 



* Prelim. Notice Lamell. 2:90 (1870).— Pal. N. Y. 5 1 . Plates and Ex- 

 planations, pi. 64. f. 19-29 (1883.) 



t Compare Pal. N. Y. 5 1 . pi. 95. f. 12. 

 X Bull. Am. Mus. Nat. Hist. 1 : 63. 



