NAPLES FAUNA IN WESTERN NEW YORK, PART 2 293 



umbonal region but crowded toward the margins, and also traces of fine 

 radial lines are to be seen, principally on the posterior and basal slopes. 

 These take on the form of slightly wavy lunes which undulate without 

 cancelatincr the concentric striae. The figure intended to show the nature 

 of this ornament on plate 63, op. cit. [fig. 1 5] is, as stated therein, incorrect ; 

 that given on plate 93, figure 29, approximates the actual condition. 



With regard to Euthydesma beyrichi Holz., Beushausen has 

 suggested the probability of its identity with E. subtextile but hesi- 

 tated to pronounce the two forms alike, because, first, of the supposed 

 " radial striation of the entire shell " in the latter, which is not perceptible 

 except with extraordinarily favorable preservation ; again, on account of 

 the cancelation of the radial and concentric striae and the formation of 

 nodes at their intersection, a condition which exists only on a minute scale ; 

 and, thirdly, because of only two posterior folds parallel to the hinge line. 

 As shown by our figures, the number of these varies from one to five. 



Habitat. Genesee province ; Chautauqua subprovince. Barcelona, 

 Correll's point, Forestville, Chautauqua co. and at Gowanda, Cattaraugus 

 co. The original specimens of Mytilarca beyrichi are from the lower 

 Upper Devonic at Martenberg, Westphalia. Beushausen further reports 

 the species from Oberscheld and from the upper Upper Devonic of the 

 Enkeberg. 



elasmatium gen. nov. 



Under this name we propose to bring together series of disconnected 

 right and left valves subtriangular or subcircular in outline, with cardinal 

 characters obsolete and surface smooth or concentrically lined. The right 

 valves are convex, arched in the umbonal region, with an oblique, low 

 umbonal ridge and well defined umbonal slope. The left valves agree in 

 marginal outline and general convexity with the right, but a vertical inte- 

 rior plate or ridge begins at the beak and divides the shell along the 

 curving middle line into two subequal parts. A lesser and similar internal 

 plate seems to lie in the place of the posterior umbonal ridge. 



Surface of both valves concentrically striate. 



