384 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.42. 



furrow or median sulcus in perfectly preserved specimens. The 

 species Modiolopsis dncinnatiensis Hall and Whitefield is taken by 

 Ulrich as genotype of his genus Whiteavesia, although we find con- 

 tained in the original definition of that species the characters upon 

 the absence of wliich the new genus was based. The specific defini- 

 tion includes the following clauses: ''Basal line gently curving 

 tliroughout its length in most cases, but in some examples becoming 

 slightly sinuate opposite or a Httle posterior to the beaks," and "an 

 obscure, shallow mesial depression extends across the valves from the 

 beaks, reaching the basal line just behind the anterior third of the 

 length."^ This is inconsistent with that part of the generic definition 

 of Whiteavesia which reads, ''Base gently convex, occasionally 

 straight, never sinuate. Mesial sulcus wanting." ^ 



Our genus Eurymyella agrees mth the generic definition of Uhich's 

 Whiteavesia in the gently convex or straight base and absence of 

 mesial sulcus, but differs from it in lacking the "radii or divaricating 

 folds" wliich are described in the definition and reproduced upon 

 the illustration given of the genotype Modiolopsis dncinnatiensis^ 

 and more distinctly expressed by M. cancellata Walcott,* wliich is 

 the second species cited as representing the genus Whiteavesia. 

 Eurymyella also differs from Whiteavesia in its liinge. Wliereas in 

 Eurymyella the liinge plate is typically veiy narrow at the sides and 

 without lateral teeth, it is fairly strong under the beaks and has a 

 cardinal tooth or teeth expressed there in both valves. It also differs 

 by its small low beaks. The beak is described as "comparatively 

 large, full, and rather prominent" in Whiteavesia. ^ 



Eurymyella very closely resembles Uhich's genus Eurymya, wliich 

 fact has suggested the name here proposed. The chief difference 

 discovered is in the liinge. The liinge of Eurymya is described as 

 "strong with a broad longitudinally striated ligamental area posterior 

 to the beaks and beneath them an obscure cardinal fold or tooth in 

 the left valve and a corresponding depression in the right." The 

 "presence of a striated ligamental area" is specifically named as one 

 of the four principal distinguisliing features, separating Eurymija 

 from Modiolopsis. The genus Eurymyella has the obscure cardinal 

 teeth under the beaks, but the lateral parts of the hinge area are, in the 

 typical forms, scarce^ more than a linear thickening of the shell 

 margin, and thus lack one of the essential characters of Ulrich's 

 genus Eurymya. 



The type-species of Eurymyella {E. shaleri) agrees still more closely 

 with Anodontopsis angustifrons McCoy in its external appearance; 



1 Pal. Ohio, vol. 2, pt. 2, 1875, p. 88. 



2 Ulrich, Geol. and Nat. Hist. Sun-. Minnesota, Final Kept., 1S94, p. 514. 



3 Ulrich, Idem, p. 514, fig. 39a. 



«Trans. Albany Inst., vol. 10, 1879, p. 22, pi. 1, figs. 8 and 8a. 



* Ulrich, Geol. and Nat. Hist. Surv. Minnesota, Final Rept., 1894, p. 514.J 



