226 PALEONTOLOGY OF THE EUREKA DISTRICT. 
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 Hamiltone and Grammysia arcuata, belong to the 
Middle Devonian in New York, and Grammysia Hannibalensis and Sangui- 
nolites AZolus 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. 
a“ 
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 striw, and that of 
the posterior by 5 or 6 narrow, radiating coste; in addition, the body of 
of the valve is marked by numerous rounded radiating costz, that, towards 
the pallial margin, become subangular, with a quite broad interspace between 
them; the concentric strize 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. 
