70 Annals of the Carnegie Museum. 



Subgenus Vogdesia nov. 



Vogdesia bearsi Raymond. 



Plate XIX, figures 10-12. 



Isotelus ? bearsi Raymond, Annals Carnegie Museum, III, 1905, 345, pi. 10, figs. 



21-24, not 25. 



Material collected since the publication of my previous paper makes 

 it possible to place this species more satisfactorily than was done at that 

 time. A few thoracic segments which appear to belong to this species 

 have been found. They show an extremely wide axial lobe, and the 

 dorsal furrows are very shallow. The thorax is thus similar to that of 

 Nileus, as is the pygidium. The cephalon, which is short and broad, is 

 also similar to that of Nileus, but differs from it in having smaller and 

 much more elevated eyes and deeper dorsal furrows. In these particulars 

 it is sufficiently different from Nileus to be put in a separate subgenus, 

 of which it is the type. 



Description. 



Cephalon broad, flattened on top, with abruptly rounded slopes. Gla- 

 bella slightly convex, extending to the frontal margin, which is abruptly 

 incurved. Between the glabella and the free cheeks are quite deep dorsal 

 furrows. The lobation of the glabella is very obscure, four pairs of very 

 faint furrows being visible on small specimens. Some of the exfoliated 

 specimens show a very faint median tubercle which is situated back of 

 the eyes as in Asaphus, not between them as in Nileus and Symphysurus. 



The eyes are far apart and project high above the general level of the 

 head. They are situated a little behind the middle of the cephalon. 

 The genal angles are rounded. 



The thorax is known only from isolated segments. The axial lobe is 

 very wide, and the dorsal furrows only slightly impressed. Pygidium 

 rounded in outline, gently convex, the axial lobe almost obsolete. Around 

 the posterior end is a rather wide depressed margin. 



Nileus vigilans (Meek and Worthen) is another species which belongs 

 to this subgenus. It has small eyes, and a faint median tubercle back of 

 them. Clarke (Paleontology of Minnesota, Vol. Ill, pt. II, p. 713) has 

 already pointed out that that species is not a typical Nileus, differing 

 from Nileus armadillo and N. palpebrosus in having smaller eyes. Dr. 

 Clarke considers the smaller and higher eyes as the accompaniment of 

 phyletic maturity in the group, and states that another name "might be 

 useful as indicating the different state of development attained by these 

 later forms." 



