I30 NORTH AMERICAN INDEX FOSSILS. 



Hamilton (Sellersburg) beds of Falls of Ohio region. 



183. P. raphanus Hall. Devonic. 

 Small, slender, gradually tapering; living chamber short, ab- 

 ruptly sloping to contracted aperture, which is equal to transverse 

 diameter of living chamber, and has a small semicircular hypo- 

 nomic sinus ; siphuncle submarginal, nummuloidal. 



Hamilton of New York, and Sellersburg beds of Falls of Ohio 

 region ( ?). 



184. P. tumidum Hall. Devonic. 

 Gradually expanding to living chamber which is inflated and 



rapidly narrows to aperture. 

 Chemung of New York. 



LXVni. Trimeroceras Hyatt. 

 Breviconic orthoceracones like preceding but with apertures 

 contracted into narrow, slit-like openings arranged in form of a 

 T-shaped cross, the stem of which forms the hyponomic sinus and 

 the arms the brachial sinuses. Siluric. 



185. T. gilberti Kindle. Siluric. 

 Large (body chamber of type: height, 83 mm.; basal diameter 



89X65 mm.), rapidly tapering, of conical form; upper side of 

 body chamber rather flat, parallel to plane of the basal edge. 

 Niagaran of northern Indiana. 



LXIX. Hexameroceras Hyatt. 

 Like the preceding but with six lateral sinuses in addition to the 

 hyponomic sinus ; no median sinus present. Siluric. 



Fig. 1378. Hexat7ieroceras herzeri.Y^y^. (Pal. Ohio. ) 



186. H. herzeri Hall and Whitfield. (Fig. 1378.) Siluric. 



Small, somewhat compressed laterally ; aperture rapidly contract- 

 ing; brachial sinuses elevated. 



Niagaran of Ohio. 



