NO. 1908. NEW SILURIAN M0LLU8CA FROM MAINE— WILLIAMS. 385 



in fact the figure 15 ^ of that species is a fairly good figure of some of 

 the large specimens collected from Eastport. Here again, however, 

 it is the hinge, as described for the genus Anodontopsis, which excludes 

 our species from the McCoy genus. McCoy describes the hinge as 

 follows: "Hinge line shorter than the shell, with a posterior, long, 

 slender tooth or cartilage plate extending just below it (double in the 

 right valve), and another similar but shorter one in front of the beaks 

 * * * (occasionally one small cardinal tooth beneath the 

 beak). "2 



In no specimen of the type-species of EurymyeUa have lateral car- 

 dinal teeth been discovered. In one species and specimen {Eurymy- 

 eUa convexa) there is seen a single short, rather oblique linear groove 

 which may be the mold of a lateral tooth near the extreme pos- 

 terior end of the hinge area. 



At the close of the definition of the species A. angustifrons McCoy, 

 we note the statement: "The posterior lateral tooth or plate extends 

 almost to the end of the hinge line and close to it." ^ It is not unrea- 

 sonable to imagine that the obscurity of the hinge characters in 

 these forms is the result of degeneration coincident with a brackish- 

 water environment forced upon a race, the normal representatives of 

 which were marine and possessed more definite development of 

 lateral teeth. In fact this interpretation is suggested by finding in 

 the lower beds on Denbow Point, associated with brachiopods of 

 strictly marine habitat, a species which expresses the generic charac- 

 ters of Eurymyella with the added characters of thickening of the shell 

 and widening of the hinge area. (See Eurymyella denhowensis, p. 390.) 

 But as a matter of strict definition of characters the typical forms 

 are, by the feeble development of the hinge characters, excluded 

 from the genera Anodontopsis, Eurymya, and Whiteavesia, which they 

 closely resemble in exterior character, and it becomes necessary to 

 erect a new genus to include them. 



Both the history of the faunas leading up to the formation in which 

 the Eurymyella appear and the associated species (Lingulas, ostra- 

 cods and a few small gastropods) and the fact that the formation is 

 terminated by unconformity, suggest that the environmental condi- 

 tions were in shallow water near the ocean, but, probably, brackish 

 and not pure salt water. 



EURYMYELLA SHALERI, new species. 

 Plate 49, figs. 1, 2, 3, 4. 



Shell rather small, tliin, fragile, compressed, subtriangular in out- 

 line; hinge line straight, long, forming with the umbonal ridge a 

 triangular flattened area or wing. Posterior and anterior extremi- 



1 Brit. Pal. FossUs, 1855, p. 271, pi. life, fig. 15. 



2 Ann. and Mag. Nat. Hist., ser. 2, vol. 7, 1851, p, 54. 

 2 Idem, p. 55. 



20441°— Proc.N.M.vol.42— 12 ^25 



