GIRTY, NEW CARBONIFEROUS FOSSILS 283 



strongly rounded. Posterior extremity obliquely truncated, projecting. Con- 

 vexity high. Umbilical pit deep, elongated but not continued to the hinge, 

 posterior to the middle. 



Primitia seminalis sp. nov. 



Shell small, transversely subovate. Cardinal line straight or nearly so, 

 converging strongly toward the front with the gently convex lower margin. 

 Anterior end sharply rounded. Posterior end broadly and rather regularly 

 rounded. Post-cardinal angle distinct. Convexity moderately high, with a 

 flattened band about the margin. This band is narrow and sharply defined 

 ai-ound the potserior portion of the shell, broad and not well defined at the 

 front end, narrow and ill defined along the middle of the dorsal and ventral 

 borders. Central pit rather large, subcircular, poorly defined, situated very 

 near the middle of the convex portion, slightly above and distinctly posterior 

 to the middle of the entire shell. 



Halliella? retiferiformis sp. nov. 



Shell small, subrhomboidal. Dorsal border long and straight. Ventral 

 border gently curved along the middle, strongly curved at the ends, con- 

 verging anteriorly with the cardinal line. Anterior extremity strongly 

 rounded. Posterior extremity more broadly rounded, subtruncate. Convex- 

 ity high and inflated at the anterior end. more gentle across the broad pos- 

 terior end. A deep, somewhat elongated pit is situated a little above and 

 distinctly posterior to the middle. It lies near the dorsal border without 

 apparently extending to it. The shell posterior to the pit is elevated into a 

 sort of low tubercle. 



Surface rather coarsely reticulate. 



Kirkbya Jones 



The genus Kirkhija has for its type the species E. permiana, which is 

 distinguished hy having somewhat the shape of a parallelogram, but with 

 the posterior end higher than the anterior. The obliquity is backward. 

 There is a subcentral muscular pit. The surface is reticulated, and the 

 free margins are provided with one or two flanges. The right valve is 

 larger than the left and overlaps it on the ventral border. With this 

 species were associated in the same genus other forms presenting very 

 considerable differences in sculpture and general expression. 



A number of species more or less resembling the English ones have 

 been found in the lower Fayetteville fauna, but they present differences 

 from one another which make it undesirable, in my judgment, to include 

 them all in a single genus. Three groups of generic or subgeneric rank 

 can in fact be distinguished. One of these seems to have the essential 

 characters of typical Kirl:bya and includes K. lindahli var. arlcansanay 

 K. oblonga var. transversa, K. rcfle.ra and K. simplex. Another group 

 which it is proposed to call Ampliissitcs has the two valves equal, neither 



