226 PALEONTOLOGY OF THE EUEEKA DISTEICT. 



added, Macrodon tenuistriata ; all the others from the Eureka District occur 

 in the lower portion of the Lower Carboniferous limestone. The relations 

 of the greater number of the species are with Devonian and Lower Carbon- 

 iferous species rather than with those of the Coal Measure Groups of the 

 Mississippi Valley. 



Two species, Macrodon Hamiltonce and Grammysia arcuata, belong to the 

 Middle Devonian in New York, and Grammysia Hannibaknsis and Sangui- 

 nolites JEolus occur in the Chemung and Waverly Groups. 



Larger collections from the localities already known in the Eureka 

 District will undoubtedly add materially to the number of species, if not 

 genera, already described, as many fragments of unidentified forms occur 

 in the collection; but with twenty-one genera, represented by forty-five 

 species, to add to those already mentioned by the above authors, the Lamelli- 

 branchiata is fairly represented in the Carboniferous system of Nevada. 



Genus AVICULOPECTEN McCoy. 



Aviculopecten Haguei, n. sp. 

 Plate xix, fig. 4. 



Shell large, oval or suborbicular in outline, exclusive of the ears; left 

 valve depressed convex, hinge-line about three-fourths of the greatest 

 width below; umbonal margins converging to the beak at an angle of 90; 

 lateral margins rounding into the regularly curved pallial margin; pos- 

 terior ear larger than the anterior, less obtuse, and not so distinctly defined 

 by the angle of the umbonal slope; the sinuses separating the ears from the 

 lateral margins are shallow, the posterior being more broadly rounded than 

 the anterior. 



Surface of each ear ornamented by fine concentric striae, and that of 

 the posterior by 5 or 6 narrow, radiating costae; in addition, the body of 

 of the valve is marked by numerous rounded radiating costae, that, towards 

 the pallial margin, become subangular, with a quite broad interspace between 

 them ; the concentric striae that are so marked on the ears are scarcely dis- 

 cernible except on the outer portions of the shell, owing to the imperfect 

 state of preservation of the outer surface. 



