146 



Cincinnati Society of Natural History. 



third the entire length of the shell, and then the shell recedes 

 regularly until it terminates at the sharply-rounded postero- 

 basal end. Anterior end rapidly contracted forward of the 

 beaks, the point of greatest length being directed a little 

 downward below a straight continuation of the cardinal line : 

 from the obtuse anterior point the shell is rounded into the 

 basal margin. Body of each valve marked by a shallow sinus 

 directed downward and backward from the umbo, and grad- 

 ually widens to the basal margin, which it serves to straighten 

 in the middle part. Posterior umbonal slope broadly rounded 

 and extending to the postero-basal margin. Anterior umbonal 

 ridge broadly rounded and indistinctly defined. 



Surface of the valves marked by concentric lines of growth 

 and stronger undulations, which are most conspicuous at the 

 anterior end and below the posterior umbonal ridge. There 

 are also radiating lines on the posterior umbonal ridge and 

 some evidence of pustules. Our specimens are casts; none 

 of the shell is preserved. There was no gaping of the shell 

 at either end. 



Found in the middle part of the Hudson River Group, on 

 the hills about Cincinnati, Ohio, and now in the collection of 

 Mr. Faber. 



Orthodesma ashmani n sp. 



Plate 8, Fig. 12, right valve; Fig. 13, left valve; Fig. 14, left 

 valve of a smaller specimen. 



Shell moderately elongate or proportionately shorter and 

 thinner than is usual in this genus, and having somewhat the 

 form of Orthodesma byrnesi. Cardinal and basal margins sub- 

 parallel, and ends rounded so as to give a longitudinal sub- 

 elliptical outline to the shell. Length, from two and a quarter 

 to two and a half times the width; valves depressed, con- 

 vex, giving the shell a thickness of less than half the width. 

 Beaks small, obtusely pointed, incurved, approximate, and 

 situated a little more than one-fourth of the length of the shell 

 from the anterior end. Cardinal line straight, posterior to 

 the beaks for more than half the entire length of the shell, 

 from which point the shell is obliquely truncated and rounded 



