.')4-i Annals of the Carne(;ie Museum. 



Description. 



Cephalon large, smooth, depressed, with a nearly flat border around 

 the front. Eyes large, situated rather far apart and about one quarter 

 the length of the cephalon from the posterior margin. Cranidium 

 shows no trace of glabellar furrows. Free cheeks large, bearing a 

 genal spine of varying length, usually not over an inch long on a 

 cephalon three inches in length — measured along the axis of the 

 cranidium. 



Thorax unknown. 



I'ygidium rounded in outline, regularly convex, with a somewhat 

 depressed border. Axis barely outlined except at the front. Ribs 

 obscure, visible only in oblique light and best seen on the cast. 



T-ength of cranidium 66 mm., width between eyes 60 mm., back of 

 eye 18 mm. from the posterior margin. A jjygidium is 79 mm. 

 long, 86 mm. wide, axis 40 mm. wide at the anterior margin. 



Locality. — The figured specimens are from the east side of Valcour 

 Island. The species is found at Crown Point, Valcour Island, Chazy 

 and Cooperville, New York. 



Isotelus obtusum Hall. {Plate 12, figures i, 2.) 



Asaphtis ? obtusits Hall, 1S47, Paleontolcgy, New York, volume i, page 24, plate 

 4 bis, figure 14. 



This species is one of the most common and most characteristic of 

 the Chazy fossils, immense numbers of abdomen shields occurring in 

 certain layers. The specimens are remarkably uniform in size, all the 

 pygidia indicating specimens of about the same length as our single 

 complete specimen, two and one half inches. 



Description. 



Cephalon short and wide, the genal angles rounded. Crlabella 

 smooth, with no trace of glabellar furrows. Eyes large, situated far 

 apart, and near the neck ring. 



Thorax of eight segments, the axis wTde and the segments turned 

 down quite sharply at the sides. Along each side of the axis are a 

 series of jiits between the segments. 



Pygidium nearly semicircular, moderately convex, with no border. 

 The axis is faintly developed and there are no ribs on the pleura. 

 Entire surface of cephalon, thorax and pygidium thickly covered with 

 large punctre, by which character the species can usually be distin- 



