Maryland Geological Survey 567 



ville Eoacl 882, 944; Thomjjsoii "rdwii-hiij, Fuhoii County, Pennsylvania, 

 1300; Yellow Springs Eun, 11-24, 11;!!). 1222 ; Millstone, TO-l, 1122, 1149. 

 CoJlecilon. — Maryland Geological Survey. 



Productella iiystricula Hall 

 Plate LI, Figs. lG-19 



Productella Iiystricula Hall, 1S67, Paleontology of New York, vol. iv, p. ITS, 

 pi. xxvi, figs. 1-8. 



Descri[)tiun. — Shell small, convexo-concave; hinge-line shorter than 

 the width of the valves, surface puckered along the hinge toward the 

 cardinal angles, wrinkles continued over the shell as fine concentric lines 

 bearing- numei'ous slender spines. Dorsal valve with pustulose concentric 

 wrinkles. 



Length 9 nun. ; width 12 nun. 



This is a very small species as preserved in the j\laryland rocks and has 

 not been found well enough retained to pennit its illustration. It may, 

 however, be recognized by its diminutive size and the abundance of hair- 

 like spines on its surface. 



Occurrence. — Jennings Formation, Chemung Member. On the 

 road over Trout Eun, 3 miles south of Oakland. 



Collection. — Maryland Geological Survey. 



Productella navicelliformis n. sp. 

 Plate LI, Fig. 20 



Descrjpiion. — Shell small, subcircrdar, length and width subequal. 

 'Hinge-line straight, a little shorter than greatest width of shell. A'entral 

 valve very gibbous, arcuate; umljo much incurved, projecting a little 

 beyond hinge-line. Point of greatest convexity posterior to middle of 

 shell, surface curving abruptly towards cardinal angles which are con- 

 cave. Dorsal valve not observed. 



Surface ornamented by closely set spinules, the bases of which are 

 linen)' and fi)rm slender interrupted costce. This species closely resembles 

 P. navicella of the Onondaga and Hamilton but differs in beiuff less 

 elongate and having a less prominent umbo. It resembles P. Iiystricula 



