FOSSILS OF T11E DEVONIAN. 



109 



1, p. 13, fig. 3. 1874), from the Gasp^ limestone, but differs in surface char- 

 acters. 



Formation and locality. In the lower horizon of the Devonian limestone 

 of Lone Mountain, 18 miles northwest of Eureka, Nevada. 



Lingula White!, n. sp. 

 Plate xiii, fig. 3. 



Shell above the average size, subelliptical in outline, the length and 

 breadth as 5 to 3; the cardinal slopes of the dorsal valve converge at an 

 angle of 20; front broadly rounded and sides subparallel, curving slightly 

 outward. The dorsal valve is quite convex and a little flattened along the 

 center towards the front. 



Surface marked by fine concentric and radiating striae, and when 

 the outer shell is partially decorticated strong radiating lines, crossed by 

 raised concentric striae, give a somewhat reticulated appearance to the sur- 

 face. The length of the specimen described is 29 mm and the breadth 1 7 mm . 



The general outline of the species is similar to that of Lingula squami- 

 formis Phillips (Mon. Brit. Foss. Brach. Davidson, vol. ii, p. i05, pi. xlix, 

 figs. 1 10), of the Carboniferous rocks, but the valves are more convex 

 and the scars on the interior of the dorsal valve differently arranged. I 

 know of no closely related Devonian species. 



A cast of the interior of the dorsal valve was obtained from a fragment 

 of limestone in which the shell adhered to the matrix by its exterior sur- 

 face and left the imprint of the vascular markings and muscular scars 

 beautifully and distinctly defined on the cast. It is of great interest, as it 

 affords the opportunity for the comparison of the structure with that of living 

 forms of the genus, and shows that the strong generic resemblance of the 

 outer surface of the shell to that of recent species is also present in the 

 more important muscular scars on the interior surface. 



At the posterior end, just within the apex of the valve, the cast of the 

 elongate divaricator muscular scar (d, plate xiii, fig. 3) is well impressed: 

 it is transverse and arches forward a little at the sides, back of the initial 

 points of the path of the advance of the posterior adductor and adjuster 



