252 rnOCEEDlNGS of the national museum. vol,. XXVIII. 



JAMESELLA, new subgenus of NISUSIA. 



There are several .species of Lower Cambrian V)rachiopods that differ 

 from Alsu.siafei<:trnata in the absence of the strong- spines on the radi- 

 atini;- ribs. This character is so marked that I separate the species 

 without it as a siibgeneric j^roup. Tlie subgeneric name is in memory 

 of Dr. Joseph F. .Tames. 



Type of subgenus, OrtJih perpasta Pompeckj. 



NISUSIA (JAMESELLA) AMII, new species. 



Ventral valve convex, elevated at the umbo, with the beak slightly 

 incurved; area high, vertical, slightly incurved; delthyrium triangular, 

 higher than its greatest width and covered by a convex deltidium, 

 which is imperforate. Surface of shell marked by numerous tine, 

 rounded, equidistant ribs that increase by interpolation; about 8 ribs 

 in a distance of 2 mm. at frontal margin. Size: Length, 8 mm,; 

 width, 10 mm.; elevation at umbo, 4 mm. 



The front margin of the deltidium broken so that it is impossible to 

 state whether it was arched as is the deltidium of Nhusia festlnata. 

 There is no trace of a foramial aperture in the deltidium. The line, 

 regular ribs and high area serve to distinguish this from other species 

 of the genus. Dorsal valve unknown. 



The specific name is that of Dr. H. M. Ami, of the Canadian 

 Geological Survey. 



Formation and locality.— \jOwqv Cambrian. I found this shell in a 

 limestone bowlder of the Sillery conglomerate in association with frag- 

 ments of Olenellus, 4 miles below Quebec, on south shore of St. Law- 

 rence River, Canada. 



NISUSIA (JAMESELLA) ARGENTA, new species. 



OnW the ventral valve is known of this species. Its outline is sub- 

 rectangular with hinge line a little shorter than the greatest width. 

 Strongly convex with a keel-like median elevation extending from the 

 incurved beak over the elevated umbo to the front margin, with gradu- 

 ally increasing width. Surface marked b}" fine, concentric stride of 

 growth and about five sharp, elevated radiating ribs on each side of 

 the two ribs on the median ridge. Area low, wdth the minute beak 

 curving down to and possibly slightly over it. 



This shell is represented by two specimens that have such strong 

 characters that 1 unhesitatingly give them a specific name. The only 

 form known to me that resembles them is N. (./.) kuthani of Bohemia. 



Formation and locality. — Lower Cambrian. In shaly limestone 

 containing fragments of Olenellus. Three miles southeast of Barrel 

 Spring, one-half mile east of road. Silver Peak District, Nevada. 



