2l8 NEW YORK STATE MUSEUM 



apical angle of spire about 6o°; fine crowded surface striae. In the 

 specimens so far obtained from the Manlius limestone, no septa have 

 been preserved. 



Found in the Manlius limestone of North Buffalo (Vogt & Piper, 

 fig. 149) and Williamsville. The species was originally described 

 from the Coralline limestone (Niagara) of Schoharie county (N. Y.) 



Class CRUSTACEA Lamarck 



Order ostracoda Latr. 



The ostracods are small Crustacea, with a bivalve, calcareous or 

 horny shell covering the entire body. The valves are joined dorsally 

 by a membrane, and open along the ventral side. The body is in- 

 distinctly segmented, and bears seven pairs of appendages, two 

 pairs of which represent the trunk limbs. The shell corresponds 

 to the carapace of the higher crustaceans. These organisms are 

 minute and will ordinarily be overlooked unless search is made for 

 them with a lens on the surfaces of the shale laminae. They are 

 specially abundant in the finer grained shales. 



Genus isochilina Jones 



[Ety. : l'ao$, equal to; xsiXog, lip] 



(1858. Can, organic remains. Decade 3, p. 197) 



Carapace with equal valves, whose margins meet uniformly and 

 do not overlap; greatest convexity central, or toward the anterior 

 end; anterior tubercle present. 



Isochilina cylindrica (Hall). Cytherina cylindrica Hall 

 (1852. Pal, N. Y. 2:14, pi. 4) 



Distinguishing characters. Oval, elongate form; great convexity, 

 " which, when both valves are joined, would give an almost cylin- 

 drical form to the shell ". 



Found in the upper Medina sandstones at Medina (Hall), but 

 probably also at Niagara and other places. 



Genus leperditia Rouault 



[Ety.: Leperdit, proper name] 



(1851. Soc. gcol. France. Bui. ser. 2, 8:377) 



Carapace with unequal valves, the right valve the larger and over- 

 lapping the left valve, along the ventral and, to some extent, along 

 the anterior and posterior ends; valves smooth, oblong and horny. 



