518 Contributions to Invertebrate Falseontology . 



L.eperditia augiilifera. 



Plate V, figs. 28-30. 



Leperditia anguUfera Whitf., Ann. N. Y. Acad. Sci., March, 1882, 196. 



Carapace of medium size, having a length, in adult individuals, of about 

 three-eighths of an inch, by a height of one-fourth of an inch in the broadest 

 part. General form of the outline broadly sub-ovate and widest posteriorly ; 

 hinge-line straight, equal in length to two-thirds that of the entire valve ; 

 anterior end a little the shortest, narrowly rounding into the broadly curved 

 basal line ; posterior end broadly rounded. Surface of the carapace highly 

 elevated and prominent, forming a strong, somewhat angular, longitudinal 

 node just within the basal margin, and near the middle of the length. From 

 this point, the surface slopes somewhat gradually upward to the hinge-line, 

 with a barely perceptible convexity, except on the anterior end, where it is 

 more strongly convex, and characterized by a rather prominent and well- 

 marked ocular tubercle. From tlie angular node near the lower margin, 

 there is, on well-preserved individuals, a perceptible angulation, extending 

 along the surface to the point of greatest length on the anterior end, and a 

 similar one, but less strongly marked, on the posterior side. There is no 

 perceptible difference in form between the right and left valves, eacli showing 

 the features about equally developed. No appearance of striations radiating 

 from the ocular tubercle can be detected, either on the internal casts or in the 

 matrices ; still the nature of the rock in which they are imbedded is such that 

 very obscure markings would scarcely be preserved. 



This species differs from Lejjerditia alta Conrad, of the same 

 formation, in its larger size, and in the larger and more distinct 

 eye-tubercle, as well as in its slightly different position ; but most 

 distinctly in the sub-angular ridge-like node, and greater convexity 

 of the lower border of the valves. This projecting node being 

 situated near the lower margin, and also being the most prominent 

 point of the valve, causes the rock to adhere to the more abrupt 

 sides when fractured, and gives to the valves as they appear upon 

 the fractured surface a very decidedly triangular aspect, entirely 

 unknown in L. alta. 



Formation and Locality. — In the hydraulic limestone of the 

 Lower Hclderberg group, at Greenfield, Ohio, where it occurs in 

 great numbers, forming distinct layers through the rock, as does 

 the L. alta in the Tentaculite limestone of New York. 



