Contrihutions to Invertebrate Palaeontology. 599 



Genus CRA\IA Retzius. 



Crania carboiiaria. 



Plate XV, figs. 11 and 12. 



Crania carboiiaria Whitf., Ann. N. Y. Acad. Sci., 1882, p. 229. 



Shell small, none of the specimens observed exceeding three-eighths of an 

 inch in diameter ; subcircular in outline, or varied in form by the outline of 

 the object to which they are attached. Free valve depressed convex, marked 

 by a few concentric lines of growth ; attached valve thin, but with a slightly 

 thickened margin. Posterior muscular impressions large and submarginal, 

 the others being nearly central and forming a small elevation just posterior to 

 tlie middle of the valve. 



The shells of this species are found attached to the spines of Zea- 

 crinus and other bodies, one of those figured being upon the oper- 

 culum of Naticopsis. They are very thin, and not easily detected in 

 the roughened condition caused by the adhering material in which 

 most of the fossils from these beds are found. Species of this genus 

 are rather rare in the Coal Measures, but very few having been 

 described. Crania Permiana Shumard, from the white limestones 

 of the Guadalupe Mts , Texas, is a large form, and probably not a 

 Crania, according to the description given. C. modesta White and 

 St. John, from the Coal Measures of Iowa, is described as "rather 

 small, finely punctate, smooth, except somewhat strong concentric 

 lines of growth toward the margins. Upper valve moderately con- 

 vex, umbo oblique, nearly central. Lower valve moderately con- 

 cave." There would appear to be some similarity between the 

 upper valves of this and the Ohio species; but the remark concern- 

 ing the lower valve being " moderately concave" throws consider- 

 able doubt on their identity, as the lower valve of this species is 

 attached over its entire surface, while that one would appear to be 

 free or partially free, if it is a Crania. 



Formation and Locality. — In the Coal Measures of Carbon Hill, 

 Hocking Co., Ohio. Collected by H. Moores, Esq., of Columbus, 

 Ohio. 



