122 SYSTEMATIC PALEOXTOLOGY 



At first it was believed that this form might be regarded as a variety 

 of CytTieridea muUeri (Mlinster), a common and wide!}' distributed 

 European Tertiary and Eecent species. However a more careful com- 

 parison brought out so many differences that it seemed best to rank them 

 as distinct species. This conclusion was confirmed by finding almost 

 unquestionable C. muUeri associated with C. perarciiafa at TToodstock, 

 while C. intermedia (Reuss) which Jones considers a close variety of 

 C. millleri, was found rather abundantly in association with specimens 

 agreeing closely with Jones' C. dehilis, at Upper Marlboro. C. perarcu- 

 ata differs from all of these forms in the restricted extent of its surface 

 markings, in wanting a mesial furro^', in its relatively greater height 

 and more strongly arcuate dorsal outline. Its edge view furthermore 

 is decidedly different, the central portion being thicker, while the ends, 

 the posterior especially, are thinner. 



Occurrence. — Xaxjemoy Fokmatiox. Woodstock. Aqttia Foema- 

 TiON. Potomac Creek. 



Collection. — Maryland Geological Survey. 



MOLLUSCA. 



Class CEPHALOPODA. 



Subclass TETRABRANCHIATA. 



Order NAUTILOIDEA. 



Suborder ORTHOCHAENITES. 



Family CLYDONAUTILIDAE. 



Genus HERCOGLOSSA Conrad. 



Heecoglossa tuomeyi n. sp. 

 Plates XVII-XIX. 



Nautilus sj). Tuomey, 1842, Amer. Jour. Sci., vol. xliii, p. 187. 

 Nautilus sp. Clark, 1895, Johns Hopkins Univ. Circ, vol. xv, p. 4. 

 Nautilus sp. Clark, 1896, Bull. 141, U. S. Geol. Survey, p. 63, pi. ix, tig. 1. 



Description. — Shell large; aperture wide, narrowing rapidly, without 

 curving to a narrow and sharply rounded periphery; ventral saddles of 



