'rklLOHlTKS OF TIIK CHAZV T J.MF.S lONK. 339 



from two to five annulations. It extends two thirds the length of the 

 pygidium. Sides of the axis nearly parallel and the posterior end 

 abruptly rounded. Entire surface outside the axis concave and smooth. 



Mcasitremeiits. — One specimen is 6 mm. wide, 3 mm. long, axis 2 

 mm. long, 2 mm. wide on anterior margin. 



Another pygidium: width 4 mm.; length 2.5 mm.; axis 1.5 

 mm. long, 1.25 mm. wide on anterior margin. 



Locality. — The specimen figured is from ]5i3, near the middle of 

 the Chazy at Crown I'oint, New York. It is in the private collection 

 of the writer. The species occurs at several localities on Valcour 

 Island. 



Genus ASAPHUS IJrongniart. 



Asaphus marginalis Hall. (Plate 10, figures 17-20, plate ii.) 



Asaphits marginalis Hall, 1S47, Paleontology of New York, X'olume i, page 24, 



plate 4 bis, figure 15. 

 Asaphus niargiitalis Emnmns, 1855, .\merican Geology, \'oliinie I, part 2, page 



235> plate 3, figure if). 



Hall's original description of this species is as follows : 



^^ Asaphus i/iai-oi/ialis (n. sj).) Caudal extremity semi-elliptical, 

 distinctly three lobed, marked by seven or eight distinct pseudo-articu- 

 lations, which are duplicate on the lateral lobes ; articulations not 

 reaching the margin, but terminating in a crustaceous marginal expan- 

 sion which is depressed or channelled near the edge as in Isoteliis ; 

 surface granulated. 



" This is a very distinctly marked fragment of an undescribed trilo- 

 bite, the distinctness of the false articulations and the deeply trilobate 

 character of the caudal extremity, distinguish it from the known 

 species of Isotehis, which it resembles in the marginal expansion and 

 general form. " 



The figure which accompanies this description shows a pygidium 

 with a narrow, raised axis and distinct ribs on the pleura, and these 

 are the characteristics of the pygidia which are here identified with 

 Hall's species. They are nearly all from one locality, the trilobite lay- 

 ers in Sloop Bay, Valcour Island, and associated with them are cepha- 

 lons of a type very rare among the American Asaphidix;. The specimens 

 figured on plate 10 arc all small, but the collection in the Carnegie 

 Museum contains about half of the cranidium of an individual, which 

 must have been at least twelve inches long and seven or eight inches 



