CONTRIBUTIONS TO PALJE ONTOLOGY. 



Bt JAMES HALL. 



I & 11. OBSERVATIONS ON THE GENEM STREPTORHYNCHUS AND STROPHODONTA. 



The illustrations for these papers not having been completed, the dis- 

 cussions upon the characters of the genera will be deferred to a future 

 report. 



The result of a critical examination of the species known in the higher 

 rocks of New York has resulted in referring to Strophomena chemungensis 

 Conrad, the following forms, which are apparently only varieties of 

 this very variable species : Strophomena hifurcata Hall, S. arctostriata 

 Hall, ;S'. pectinacea Hall, Orthis perversa Hall, Streptorhynchus pandora 

 Billings, Orthisina arctostriata and 0. alternata Hall, Orthis ineqaalis and 

 O.pravus Hall. 



Among these there are noticed as distinct varieties, the following : 



a. Stre])torhynchus 'pandora Billings, which differs very little from 

 S. woohvorthana Hall of the Lower Helderbera: 







group. 



b. 



8. 



arctostriata Hall; 



c. 



S. 



perversa Hall; 



d. 



8. 



pectinacea Hall. 



These varieties of form and of surface-markings are illustrated on 

 Plates iv, ix and x of Vol. 4, Palaeontology of New York. 



The study of the hinge structure in some forms referred to the Genus 

 Strophodonta has suggested some modifications in the limits of the 

 genus, and indicates in one direction an intimate relation with Streptor- 

 hynchus. 



