Mauylaxd Geological Survey IGl 



middle, liniadly tniiicatf on the uinh'), regularly curving to the front, 

 abruptly depressed at the sides, and forming narrow flattened ears at the 

 cardinal extremities. Dorsal valve moderately concave, minutely truncate 

 at the apex, the interior wrinkled and pustulose with a conspicuous' de- 

 pression at the umbo, and a short bifurcating cardinal process. Surface 

 of the ventral valve wrinkled at the hinge-line, marked by a greater or less 

 numl)er of spiniferous ridges, supporting slender spines of moderate 

 length; there is usually a row of two or three spines on the ears just 

 below the hinge-margin, and they are often closely arranged about the 

 limits of the truncation on the umbo, and more sparsely on the middle 

 and front part of the valve ; the dorsal valve is wrinkled along the hinge- 

 line, and the surface covered by numerous elongate spiniferous pustules, 

 bearing, when perfect, long slender spines 



This species is not common in ]\Iaryland but the argillaceous shales 

 of Evitts Creek below Wolfe Mill have furnished several specimens of 

 dorsal valves as well as the dark gray impure limestone at the iron bridge, 

 44 miles northeast of Oldtown. Part of the specimens are internal im- 

 pressions of the don^al valve which show very well its wrinkled and pus- 

 tulose character. The specimens agree quite closely Avith some of the 

 type specimens from New York, especially with the one represented by 

 fig. 23 on pi. xxiii, vol. iv, Palaeontology of New York. A gibbous ventral 

 valve from the Williams Koad about ^ mile east of the Queen City Hotel, 

 Cumberland, is referred to this species although it is not conspicuously 

 truncated and tliere are four spines in the row just lielow the hinge-line, 

 but the surface shoAvs a number of ridges upon which at some distance 

 apart are bases of spines. This species is recognized by its small size, 

 gibbous and truncate ventral valve, flattened cardinal extremities, slightly 

 concave dorsal valve whicii is wrinkled and pustulose on the interior, and 

 the scattered surface spines on both valves. 



Kindle states that this is a very common and widely distributed species 

 of the Onondaga fauna, occurring both in the soft shales and the hard 

 limestone beds. 



Length, 3-9 mm. ; width. 3-1 "2 mm. 

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