66 Annals of the Carnegie Museum. 



is quite different from that of the typical Isotelus, being shorter and more 

 evenly convex, and the hypostoma, as pointed out by Schmidt, differs 

 markedly from the typical form in having a constriction at the front. 



Description. 



Cephalon short, wide, gently convex, with a narrow concave border in 

 front. The eyes are situated nearly half-way to the front, and very far 

 apart. Dorsal furrows broad and shallow, extending to the palpebral 

 lobes. Glabella not defined, and glabellar furrows absent. Free cheeks 

 large, with strong spines at the genal angles. 



Thorax of eight flat segments, the axial lobe a little more than one-half 

 the total width. 



Pygidium broader than long, with rounded outline. It is strongly 

 convex, with a steep, concave border. Axial lobe wide at the anterior 

 end, scarcely defined by dorsal furrows, but rather prominent at the poste" 

 rior end. There are very slight traces of rings and ribs. 



Length of a cranidium in the collection of the Geological Survey of 

 Vermont, 65 mm.; width between eyes, 50 mm.; back of eyes 19 mm. 

 from the posterior border of the cephalon. These measurements corre- 

 spond rather closely with the measurements of a cranidium from Valcour 

 Island given in the original description. The type pygidium is 67 mm. 

 long and 95 mm. wide. One of the pygidia from Isle La Motte is 85 mm. 

 long and 125 mm. broad. 



Locality. — This species is found at Crown Point, Valcour Island, Chazy, 

 and Cooperville, New York, and on Isle La Motte, Vermont. 



Isotelus platymarginatus sp. nov. 

 Plate XVII, figures 2-5; Plate XIX, figure 3. 

 Isotelus harrisi Raymond, Annals Carnegie Museum, III, 1905, pi. 12, fig. 4. 



Associated with the preceding there is a smaller and more typical 

 Isotelus. This species has a nearly circular pygidium, the concave border 

 is very wide and almost flat, and the eyes are situated well back on the 

 cephalon and are not farther apart than in Isotelus gigas. In the collec- 

 tion made by Prof. Perkins is a natural mould of a small but nearly com- 

 plete specimen. 



Description. 



Cephalon gently convex, with a wide concave border. The cranidium 

 is depressed in front of the eyes, the glabella smooth, not defined, gla- 

 bellar furrows absent. Eyes large, situated a little more than their own 



