20 , NEW YORK STATE MUSEUM 



shows no traces of true dissepiments and differs from Callograptus 

 by its projecting thecal apertures. It is obvious that Dictyo- 

 n e m a f u r c i f e r u m forms, together with the Swedish species 

 mentioned above, a well-defined group which, in consideration of 

 the generally conceded collective or polyphyletic nature of the 

 genus Dictyonema and the resulting necessity of dividing this 

 genus into its components, should be recognized as a separate 

 generic unit. We propose for it the name 



Airograptus 

 (Etym. aipim to grasp, y/id<f>uj to write) 



The genus is characterized by flabelliform or shrublike rhab- 

 dosomes, projecting thecae of the general type of Dictyonema, 

 but whose apertwral processes are developed into furcate or peltate 

 terminations that attach themselves to the neighboring branch. True 

 dissepiments are absent or rare. Genotype : Airograptus 

 furciferus (Ruedemann) . Here also belong A . tuber- 

 osus, cervicornis, peltatus, cavernosus ( Wiman ) . 



The chief interest attaching to this species is that regarding its 

 geologic age, for it has been found on one hand in the long Deep 

 Kill section of graptolite horizons and in the other in the Belle- 

 fonte section of Pennsylvania which is the most complete Beekman- 

 town section in the Appalachian region. It should therefore permit 

 the correlation of at least one graptolite horizon with one of the 

 formations of the Bellefonte section. The latter has been described 

 by Ulrich in the Revision of the Paleozoic Systems, page 627. We 

 learn there that the total thickness of the Canadian in this section is 

 4232 feet, the formations distinguished being, from the base upward : 

 the Stonehenge limestone, the Nittany dolomite, the Axeman lime- 

 stone and the Bellefonte dolomite. Hahn, on the authority of 

 Victor Ziegler, reports that the graptolites were obtained " 2000 

 feet from the bottom of the limestone series which is referred by 

 Collie to the Beekmantown," which would bring the graptolite 

 horizon near the top of the Nittany or the base of the Axeman. 

 Prof. Thomas C. Brown has kindly informed the writer that the 

 graptolite horizon is located near the top of the Nittany formation. 

 Ulrich states (op. cit. p. 660) that "pending further study, it may 

 be said that the Fort Cassin fauna seems to be represented in the 

 Axeman limestone and in the upper part of the Nittany dolomite 

 by Syntrophia lateralis, Raphistoma compres- 

 sum, Trochonema exile, Maclurea affinis, 

 Bathyurus caudatus and Ribeiria compressa." 



