Contributions to Invertebrate Palaeontology. 517 



and parallel to the anterior and posterior margins of the segments, 

 instead of being irregularly disposed, as in all other species de- 

 scribed. No indication of the longitudinal rows of larger pustules, 

 marking the median line of the thoracic segments, can be traced. 

 Caudal spine not observed. 



OSTRACODA. 

 Genus L,EPERDITIA Rouault. 



Leperditia alta. 



Plate V, fig. 27. 



Cytherina alta (Con.) Vanuxera, Geol. Kept., 3d Dist. N. Y., 1843, p. 112, fig. 6. 

 Leperditia alta (Conrad) Jones, Ann. and Mag. Nat. Hist., vol. 17, 2d series, 



p. 88; Hall, Pal. N. Y., vol. 3, p. 373 ; Meek, Pal. Ohio, vol. 1, p. 187, 



pi. 17, fig. 2. 



Valves of the carapace transversely snb-ovate, widest posterior to the middle 

 and narrowed in front, the proportional height and length being somewhat 

 variable, but are usually about as two and three. Hinge-line straight nearly 

 two-thirds as long as the entire valve, extremities salient. Anterior end of 

 the valves narrowly rounded and the posterior extremity broadly curved ; 

 basal-line curved but with a scarcely perceptible angularity just posterior to 

 the middle of the length. Surface prominently convex and a little the fullest 

 anterior to the middle ; occular tubercle small, situated a little below and 

 just behind the anterior extremity of the hinge-line. Lower margin of the 

 valves slightly inflected, and in some cases the posterior margin appears to 

 have l)een bordered by a slightly thickened rim. 



The individuals examined are either internal casts or impressions 

 of the exterior, owing to which fact the finer surface features of the 

 crust cannot be definitely ascertained ; enough is seen however to 

 show its identity with tho.se from the Tentaculite limestones of 

 New York. The species as described by Mr. F. B. Meek includes 

 this and the following one, which are very distinct species, the dif- 

 ferences being very strongly marked in the great prominence of 

 the lower part of the valves of that one, and its strongly sub- 

 angular form as well as in its greater size. The principal variation 

 noticed among the individuals of this species, is in the greater 

 proportional length of some of them, producing a cylindrical form. 

 This feature is however seen occasionally among those from Scho- 

 haire, N*. Y., but does not appear to be worthy of specific consideration. 



Formation and Locality. — In the hydraulic limestone of the 

 Lower Helderberg group, at Belleville, Sandusky Co., Ohio. 



