520 Systematic Paleoxtology 



that we have no hesitancy in referring the species as above. Compared 

 with other American Paleozoic ostracods, there is none with which it could 

 be confounded. The sharp, superficial crests, together with the loose and 

 somewhat irregular reticulation of the surface, give the valves a very- 

 striking aspect. 



Length of an average right valve 1.30 mm. ; height of same .70 mm. 



Occurrence.— Helderberg Formation, Keyser Member. Cumber- 

 land. 



Collections.— MAvyland Geological Survey, U. S. National Museum. 



Genus HALLIELLA Ulrich 



Halliella ? seminulum var. longa n. var. 

 Plate XCV, Fig. 16 



Description. — Carapace elongate, nearly semicircular in outline, with a 

 long hinge-line, subequal ends, the posterior one more nearly vertical than 

 the anterior which begins to curve backward from the prominent dorsal 

 angle ; beak deeply notched ; ends and ventral side with a smooth, concave 

 border, widest posteriorly and narrowest antero-ventrally ; surface strongly 

 convex, reticulated; notch or sulcus deep, rather abruptly impressed, 

 centrally situated, vertical, extending from the dorsal edge more than half 

 across the valves. 



Length of entire carapace 0.9G mm.; greatest height 0.52 mm. 



This American variety of H. ? seminulum is more elongate even than 

 the Gotland variety of the species, which is longer than the Wenlock speci- 

 mens to which Jones originally applied the name, and the German form 

 subsequently referred to the species by Krause. Our variety differs further 

 from the European varieties in the sulcus which is more sharply defined, 

 or, to express it differently, more abruptly impressed. 



On two previous occasions,* the senior author referred Primitia semi- 

 nulum Jones to his genus Halliella, but in the second instance it was 

 recognized that the proposed generic change was not wholly natural. The 



'Jour. Cincinnati Soc. Nat. Hist., vol. xiii, 1891, p. 49; Geol. and Nat. Hist. 

 Surv. Minnesota, Final Rept., vol. iii, pt. ii, 1894, p. 656. 



