568 Systematic Paleontology — Upper Devoxiax 



from which it differs in being less transverse, more gibbons with less 

 conspicuous spinules, the bases of which form more distinctly elevated 

 interrupted costse. It differs from the other species of the fauna in its 

 smaller size. 



Length 10 mm.; width 11 mm. 



Occurrence. — Jennings Formation, Parkhead MKiiBER. AVilliams 

 Eoad, oast of Cumberland, 1466 common; roadside, 1 mile north of 

 Eocky Eun ? 



Collection. — Maryland Geological Survey. 



Genus PRODUCTUS Soweiby 



Subgenus MARGINIFERA Waagen 



Productus (Margixifera) iiallaxus Walcott 

 Plate LI, Figs. 21-23 



ProducUis (lissimiUs Hall, 1S58, Geology of Iowa, vol. i, pt. ii, p. 497, pi. ill, 



fig. 7. 

 Productus (Productella) JiaUanus Walcott, 1885, Paleont. of the Eureka 



Dist., p. 130, pi. xlii, fig. 17. 

 Productus (Marginifera?) dissimilis Hall and Clarke, 1S92, Paleont. of New 



York, vol. viii, pt. i, pi. xviia, figs. 11, 12. 



Description. — Shell subcircular, strongly convex; surface of ventral 

 valve bearing distinct radial striae interrupted by occasional growth lines, 

 spines few, erect and irregularly scattered. Dorsal valve with no radial 

 surface lines or spines but with sharply defined and regular concentric 

 ridges. On the interior the umbo-lateral areas are flat and denticulated 

 along ridges diverging obliquely from the beaks. 



Length 12 mm. : width 14 mm. 



Tin'?; shell, first described from the up]ier Devonian of Eockford, Iowa, 

 has been more recently identified in Xevada (Walcott, loc. cit.) and in 

 the lower beds of the Chemung in western Xew York.* In the material 

 described from Maryland the shell has seldom been observed, but its 

 occurrence is undoubted as the characteristics of the species are sharply 

 defined. The exterior of a dorsal valve figured bears the phar]i con- 



' Clarke, Bull., U. S. Geol. Survey, No. 16. 



