GUELPH FAUNA IN THE STATE OF NEW YORK 39 



MOSOMBEELLA BllHngS. 1 87 1 



Monomerella noveboracum sp. nov. 



Plate 2, fig. 1-6 ; plate 3, fig. 1-7 ; plate 4, fig. 38 



Shell large, thick ; brachial valve subovate ; pedicle valve elongate, 

 subovate in marginal outline, the greatest width at midlength or sometimes 

 a little in front of it, thence tapering with convex sides to a bluntly triangu- 

 lar erect umbo ; the brachial valve broader, blunter and more curved than 

 the pedicle valve. Pedicle valve gently convex, almost straight in profile ; 

 brachial valve strongly convex, with the greatest prominence posterior to 

 the middle. The surface ornamentation consists of conspicuous growth 

 lines. 



Pedicle valve. Cardinal area large, broad, flat, elongate triangular, 

 slanting obliquely inward and divergent from that of the brachial valve ; 

 subdivided longitudinally into a broad, flat, depressed median area (pedicle 

 groove) bounded by lateral ridges and broad, smooth areal borders. Median 

 area higher than broad, crossed by coarse, lamellose growth lines. Supra- 

 cardinal slope narrow, very oblique and incurved ; cardinal faces narrowly 

 triangular, curving outward, merging into a prominent and very broad car- 

 dinal buttress, which extends nearly the entire length of the platform. 

 Hinge transverse, much depressed. Platform well developed, extending 

 about half the length of the valve, linguate, widening slightly anteriorly ; 

 front obliquely and obtusely angular. Umbonal chambers in most speci- 

 mens very deep, wide mouthed and broad. Platform vaults not developed. 

 Crescent distinct below the hinge line ; lateral and terminal parts readily 

 distinguishable, the latter more impressed. Transverse scars forming an 

 oval impression between terminal crescents and platform. Platform scars 

 finely and obliquely striated ; extending apparently the full length of the 

 umbonal chamber. Umbo-lateral scars not distinguished. A broad, low 

 ridge extends from the anterior edge of the platform to the front margin of 

 the valve. 



Brachial valve. Shorter by nearly one third than the pedicle valve, 

 broadly ovate, with a low, rotund beak, and transverse hinge which is 



