10 AMERICAN JOURNAL 



genus, a marginal gape or opening for the byssus, which is finally 

 closed, but leaves a conspicuous scar from the extremity of the 

 hinge margin to the foramen, as represented in the figure. The 

 exterior of the valves shows no trace of this scar, but it is well 

 marked within and terminates in a rounded foramen. 



UNIONID^. 

 PRISCONAIA, Conrad. 



Deseri2?tio7i. — Equivalve, ovate ; hinge in left valve with two 

 cardinal teeth, the anterior one compressed, angular, obli<|ue, 

 with an anterior pit ; posterior tooth broad, smooth, convex, 

 triangular, situated under the beak, emarginate at base and di- 

 rected towards the posterior extremity ; no lateral teeth ; muscu- 

 lar impressions situated near the cardinal line ; pallial line 

 entire. 



The specimen of this shell consists of one left valve, which is 

 thin and converted into iron pyrites. It bears the same generic 

 relation to Carbonicola, M"Coy, that 3Iargaritcma bears to Unio, 

 and it existed in the same period with Carbonicola, the Carboni- 

 ferous. It can be distinguished externally from the latter genus 

 by its comparatively short ovate outline. 



Peisconaia ventricosa, Conrad. 



Description. — Ovate ; umbo broad, inflated, with a prominent 

 summit ; posterior hinge margin very oblique, posterior margin 

 obliquely truncated, extremity obtusely angular, anterior margin 

 obtusely rounded, beaks smooth and entire, distant from the 

 anterior end. 



G-resslya ventricosa ? Agassiz. 



Locality. — Little Stranger Creek, ten miles from Fort Leaven- 

 worth, Kansas. 



Observations. -r—^Yn?, fossil was found by Henry Lamborne in 

 an ash-colored shale. The hinge is in a perfect state of preser- 

 vation, and the valve became easily detached from the cast. It 

 is named from its supposed identity with Gfresslya ventricosa, of 



