158 PROCEEDINGS OF THE PALEONTOLOGICAL SOCIETY 



The presence of intervening strata of different lithologieal character, con- 

 taining in some cases fossils of Ordovician and Silurian ages, between the 

 Cambrian limestone and the Jefferson limestone, as noted by various writers, 

 iu sections in neighboring regions to the west and southwest, points to a 

 stratigraphic overlap which involves a hiatus in sedimentary record for the 

 i-egion about Three Forks. 



The Three Forks formation overlies the Jefferson limestone in this region, 

 but differs greatly in its lithologieal characters from north to south. In the 

 type region at Three Forks and to the north, along the Missouri River, it 

 consists of seven fairly distinct shale and limestone members, the upper five 

 of which are generally fossiliferous and contain a late Devonian faunule. In 

 the southern sections the formation is chiefly limestone and sparsely fossilif- 

 erous. The Three Forks formation is not nearly so widely distributed as the 

 Jefferson limestone or the overlying Madison limestone. 



The next paper was given by the senior author and illustrated by lan- 

 tern slides; 20 minutes. Discussed by E. S. Bassler and E. E. Cumings. 



STUDIES OF THE MORPHOLOOY AND HISTOLOGY OF THE TREP08T0MATA 



(M0NTICULIP0R0ID8) 



BY E. B. CUMINQS AND J. J. GAIXOWAY 



(Abstract) 



This paper is a minute study of wall structure, with reference to its 

 taXonomic significance; of the exact nature and function of aeanthopores in 

 the genus Dekayia; of certain peculiar cystlike structures in a number of 

 genera ; of communication pores iu numerous genera, and of the structure and 

 relationships of the recent sponge genus, Merlia. 



Then followed a paper presented by the author, with diagram ; 30 

 minutes. Discussed by John M. Clarke, with reply by the author. 



HAMILTON GROUP OF NEW YORK 

 BY A. W, GBABAU 



(Abstract) 



The various subdivisions originally made by the author for the Hamilton of 

 Eighteen-mile Creek have been correlated with a similar number of subdi- 

 visions in central New York by the New York Survey. The validity of this 

 correlation will be considered and the facts suggesting that an error has been 

 made will be given. A new series of names for these subdivisions will be 

 proposed. A brief comparison with the Traverse group of Michigan will be 

 made. 



The next paper was read by the author; 15 minutes. Discussed by 

 C. J. Sarle, Charles Schuchert, J. M. Clarke, M. Y. Williams, Charles 

 Prosser, and Henry M. Ami. 



