SUBCAEBONIFEEOUS PERIOD. 89 



low groove; a little more than one quarter of the length of the fissure from 

 its apex closed by a slightly convex pseudo-deltidium. 



Dorsal valve moderately convex, differing in degree of convexity in 

 different directions from its middle, but is somewhat regular in all; front 

 margin broadly and regularlj^ rounded, except that the lateral extremities 

 are more or less extended, and the central portion is emarginate by the 

 infolding of the mesial sinus of the ventral valve; mesial fold moderately 

 elevated, well defined from front margin to the beak, and increasing rapidly 

 in width from beak to front. 



Sm-face of both valves marked by from fourteen to eighteen rounded 

 2)lications on each side of the mesial field and sinus, which become less 

 distinct toward, and disappear upon, the lateral extremities ; surface of both 

 mesial fold and sinus plain, except that, in common with the surface of all 

 other parts of the shell, it is marked by fine concentric lines of growth. 

 Shell-substance distinctly punctate. 



Breadth along the hinge-line, nearly fom- centimeters ; height from 

 ventral beak to dorsal umbo, eighteen millimeters ; length from hinge to 

 front margin, sixteen millimeters. 



The transverse plate connecting the dental laminse, together with the 

 tube, which it bears along the middle of its under surface (characters that 

 distinguish the group of spiriferoid shells which Professor Winchell has 

 separated under the generic name of Syrinjjotliyris)^ are concealed by the 

 stony filling of our specimens ; but as they possess the other characteristics 

 of that group, those mentioned are doubtless present also. So far as external 

 characters are concerned, no specific difference can be detected between 

 our shell and Syringotliyris Halli Winchell {he. cit). His type-specimens 

 were obtained from strata of the Kinderhook formation at Burlington, Iowa, 

 and Clarksville, Missouri. Those of Professor Hall were obtained from the 

 same strata at the first-named locality. The want of material difference 

 between the dorsal valve of Professor Hall's species (the only part of the 

 shell described and figured by him) and the corresponding part of Professor 

 Winchell's specimens, together with the fact that they are associated in the 

 same strata at one of the typical localities, leaves little cause for doubting 

 the specific identity of Syriiigothyris Halli and S])irifer extenuatus. 



