so NEW YORK STATE MUSEUM 



width in front, while posteriorly it narrows conf^iderably. The 

 ribs of the marginal area are finer than in the preceding species. 

 On account of the posterior convexity of the body* of the valve 

 and the inequilateral development of the marginal area, the 

 entire valve has a strongly symmetric appearance. 



Dimensions. Length 2.4 mm; bight 1.7 mm; thickness .0 mm. 



Horizon and locality. Gray limestone of Rysedorph hill. 

 (Group 7) 



There is no species kiiowTi to the writer which is suggested by 

 this form. If the development of the sulcus is taken into cooisid- 

 eration, it seems to stand at the end of a series which begins with 

 such forms as E. b u 1 b i f e r a, where the sulcus is deep 

 and long and begins at the cardinal line. It then begins 

 to wander vent rally, till it ajipears as a crescent-6hai>ed pit only, 

 separate fmm the cardinal line as in E . g r a n o sa and in E . 

 s o 1 i d a ; it farther becomes faint, and may eventually disap- 

 l>ear entirely- as in E . o b 1 i q u a . At the same time the forms 

 with faintly developed sulcus have more rotund valves, 

 and mostly a convex instead of a concave marginal area; they 

 form, hence, apparently a natural gix^up of siK?cies, which event- 

 ually may be advantageously comprised under a subgeneric tenn. 



pRiMiTiA Jones & Holl 



Primitia mundula Miller rar. jonesi rar. nov. 



P r i m i t i a m u n d u I a S. A. Miller. Cin. quar. jour. sci. 

 2:350, and Ulrich, Cin. soc. nat. hist. Jour. 1800-91. 13:132 



PI. 7, fig. 2-5 



The conglonu-rate affords very minute representatives of the 



genus Primitia, which have been found to belong all to one 



tyi>e that probably stands in vnriptal relation to Primitia 



mundula S. A. Miller. 



Diagnosis. CarafKice very minute, strongly convex, subquad- 

 rate-ovate, dorsal margin hmg, straight; anterior cardinal angle 

 obtusely rounded, posterior a little less obtuse; anterior mar- 



