DESCRIPTION OP GENERA AND SPECIES. 22,5 



OSTRACODA. 



Genus ALUTA Matthew. 



Aluta bergeroni ( Walcott) . 



Plate 23, Figure 10. 



Bradoria bergeroni WALCOTT, 1905, Proc. U. S. Nat. Mus., vol. xxix, p. 99. (Species described as 

 below.) 



General outline broadly semielliptical. Hinge-line straight, nearly as wide as 

 the breadth of the valve ; anterior cardinal angle about 80 ; posterior cardinal angle 

 slightly obtuse ; the anterior margin is very slightly curved from the angle to where 

 it merges into the broadly rounded front; posterior margin somewhat broadly 

 rounded from the angle to the front. Surface convex, the greatest convexity being 

 back of the transverse center between the ocular tubercle and the posterior fourth 

 of the valve. From this elevated portion the surface slopes rapidly and somewhat 

 abruptly to the hinge-line and more gently to the lower margin. From the anterior 

 cardinal angle a very short, narrow ridge extends to a small, circular, slightly 

 elevated tubercle which is situated about an equal distance from the hinge-line and 

 the anterior margin. The anterior, posterior, and lower margins have a narrow, 

 rounded rim that is slightly flattened on the inner side. 



Surface marked by shallow, scattered punctae and very fine punctae, as seen 

 under a strong lens. 



Width of valve, 1.8 mm.; length, i mm.; depth, about 0.5 mm. 



This species is distinguished from Aluta sterope [p. 227] by its greater width and 

 the form of the ocular tubercle. 



Formation and Locality. Middle Cambrian: (032) A fine-grained bluish-black 

 limestone bowlder believed to have come from the lower part of the Ki-sin-ling 

 limestone [Blackwelder, igoyc, p. 272] ; collected in river drift i mile (1.6 km.) south 

 of Chon-p'ing-hien, on the Nan-kiang River, southern Shen-si, China. 



Collected by Bailey Willis and Eliot Blackwelder. 



Aluta enyo (Walcott). 



Plate 23, Figure 11. 

 Bradoria enyo WALCOTT, 1905, Proc. U. S. Nat. Mus., vol. xxix, p. 99. (Species described as below.) 



General outline irregularly oval. Hinge-line about four-fifths the width of 

 the valve; anterior cardinal angle nearly a right angle; posterior cardinal angle 

 slightly obtuse; the anterior margin extends from the angle almost directly down- 

 ward to where it curves and merges into the broadly rounded lower margin; pos- 

 terior margin very slightly rounded from the angle downward to where it curves 

 and merges into the lower margin. Surface moderately and uniformly convex, the 

 highest portion being near the center; a very short, narrow, low, and somewhat 

 obscure ridge extends obliquely inward from the anterior cardinal angle to a small, 

 slightly elevated ocular tubercle ; a slight furrow appears to extend from the tubercle 

 obliquely to a point about midway of the hinge-line ; a little posterior to this, and 

 near the hinge-line, there appears to be a minute, low tubercle. 



The surface appears to be minutely punctate under a strong lens. 



Width of valve, i mm.; length, 0.75 mm.; depth, about 0.25 mm. 



This species is distinguished from A. sterope [p. 227] by the difference in the 

 form of the anterior cardinal angle and the position of the ocular tubercle. The 



