150 PALEONTOLOGY OF THE EUREKA DISTRICT. 



Genus ATRYPA Dalman. 



Atrypa reticularis (Linnaeus sp.) Dalman. 

 Plate xiv, figs. 6, 60, &. 



Synonyms: See Davidson's Monographs of the British Silurian and Devonian Brachi- 

 opoda. 



This extremely variable species is represented by three distinct types 

 in the collections from the Eureka District and Lone Mountain. 



The first is a large, robust form similar to that occurring in the Upper 

 Helderberg limestone and Hamilton shales of New York, and designated 

 by Mr. Vanuxem as Hipparionyx (Atrypa} consimilaris, and is illustrated as 

 a variety of Atrypa reticularis (Pal. N. Y., vol. iv, p. 319, pi. lii, figs. 9-12). 



The variations from this, as shown on the following plate (foe. ce), also 

 occur at the lower horizon of the Devonian limestone at County and 

 Woodchoppers Peaks, Sentinel Mountain,, Eureka District, and Lone 

 Mountain, 18 miles northwest of Eureka, Nevada. 



* The second variety is more symmetrical and has very fine radiating 

 costa3, resembling the variety from the Hamilton and Chemung Groups in 

 the State of Iowa. The radiating costse, however, are finer, approaching 

 in this respect the radiating striae of the Silurian shell Zygcspira Headi Bil- 

 lings (Pal. Ohio, vol. i, p. 127). It is found in the upper part of the De- 

 vonian at Rescue Hill, at the mouth of Packer Basin, and at The Gate, north- 

 west of Eureka. 



The third variety also occurs in the higher beds of the formation at 

 The Gate and east of the Sugar Loaf. In form it is similar to the Silurian 

 examples from the Niagara limestone of New York (Pal. N. Y., vol. ii, p. 

 270, pi Iv, figs. 5 Or-u). An illustration of it is given on plate xiv, figs. 6, 

 6 a, &, of this report. 



Formation and locality. Throughout the Devonian limestone of the 

 Eureka District. 



Atrypa desquamata Sowerby. 



< 



Plate xiv, figs. 4, 4 c. 



Synonyms: See Davidson's Monograph of British 1'ossil Brachiopoda, vol. iii, pt. 6, 

 p. 58, pi. xi, figs. 1-9. 



Several examples of a species of Atrypa, with a distinctly defined area 

 and circular foramen on the ventral valve, were found in the lower beds of 



