No. 109.] Ill 



Strophomena ( Strophodonta) crenistria. 



Pal. N.Y. Vol. iv. 



Strophomena crenistria, Hall : Rep. Geol. 4th Dist. New-Tork, pa. 171, 



pi. 35, f. 3 & 4. 



Shell somewhat semicircular, much codnpressed ; length from 

 two-thirds to three-fourths as great as breadth ; hinge crenulated, 

 nearly or quite equal to the greatest width of the shell, and 

 sometimes having small salient angles at the extremities : dorsal 

 valve unknown : ventral valve much compressed. Surface 

 marked by fine striae, increasing by bifurcation and interstitial 

 addition ; crossed by fine closely set concentric lines of growth 

 and a few indistinct wrinkles, giving a subcrenulate aspect to 

 the radiating strise : interior granulose -, granules on each side 

 of thQ fan-shaped vascular impression, larger than those nearer 

 tlie margins. 

 This shell has much the form and general aspect of LeptcBna pluristriata 



( Conrad ) from the Hamilton group, but has rather coarser and more 



rounded striae, •which are not so sharply crenulated. 



Geological position and locality. Limestone of the Upper Helderberg 



group, WilliamsYille, N.Y. 



* t 1 



V 



Strophomena crenisteia. 



Strophomena ( Strophodonta) ampla. 



Pal. N.Y. Vol. iv. 

 Shell large, transverse, nearly semicircular; hinge-line crenulated, 

 equal to the greatest width of the shell : dorsal valve prominent 



