M2 



Cincinnati Society of Natural History. 



fossils are at one time and how common they may afterward 

 become. The present year, notwithstanding the place had 

 been hunted over many times by the authors, Mr. Faber 

 walked over the exposure at which the original Sphenolium 

 cuneiforme was found, and picked up another cast, nearly as 

 good as the original, and also part of the valves of another 

 specimen, one of the valves of which is illustrated with this 

 article, and which also shows part of the hinge line that is 

 illustrated. And to nearly complete our knowledge of the 

 shell of this genus Mr. Miller, on a trip to Richmond, Ind., 

 the present Summer, obtained a specimen of Sphenolium 

 richmondense, preserving almost the entire shell in a rare 

 state of preservation. We propose now to describe the shells 

 of both species. 



The shell of Sphenolium cuneiforme is marked with strong 

 concentric lines of growth, that, on account of the thickness 

 of the shell, do not seem to have made any impression on the 

 casts. The beaks are acute, incurved over the external hinge 

 ligament and approximate. The antero -basal part of the 

 shell extends a little further forward than the beaks. The 

 umbones, though high, are somewhat flattened, and there is 

 an undefined shallow depression toward the basal margin that 

 separates the well-defined posterior umbonal slope from the 

 imperfectly-marked anterior umbonal ridge. The cardinal 

 line is directed, at a high angle, from the basal margin ; the 

 shell at the hinge is very thick, and each valve bears a wide, 

 concave furrow, with longitudinal ligamental lines, for the 

 attachment of a strong external ligament. Our specimen 

 shows no evidence of teeth or sockets of any kind. 



The shell of Sphenolium richmondense is proportionally 

 much the shorter, and is marked with much finer concentric 

 lines of growth, which are almost obsolete over the umbones, 

 and the shell being thick, the}' have left no impression on the 

 casts. The beaks are acute, incurved over the strong external 

 ligament, and approximate at the extreme anterior end of the 

 shell. The umbones are higher than in Sphenolium- cuneiforme, 

 and the thickness of the shell, through the .umbonal region, 

 is greater than the height from the basal line to the cardinal 

 margin. The greater thickness of the shell is between one- 

 third and one-half the entire length from the anterior end. 



