CRUSTACEA. 125 



it represents a definite specific variation from other tonus included under this 



genus. Its distinctive characters are the broad, explanate pleura? and the axial 

 row of nodes. 



The general proportions of the pygidium are similar to those of Proetus Rowi, 

 P. darns and P. Prouti, but from all these it differs in its axial row of nodes 

 and more conspicuously sulcate annulations. From P. macrocephalus, which 

 often bears nodes upon the axis of the pygidium, it varies in the more numerous 

 annulations and greater proportional length of the former. 



Distribution. Hamilton group. In the sandy shales, Albany county. 



Proetus Phocion. 



PLATE XXV, FIGS. 9, 10. 

 Proitu.? Phocion. Billijc.s. Pakeozoic Fossils of Canada, vol. ii.'y.l. 1. p. 63, fig\ 31. 1S74. 



General Form and Proportions. One of the type specimens, which is a cast 

 of the lower surface of an entire extended individual, indicates a body rela- 

 tively broad and short, and more depressed upon the axis and pleurse than 

 P. Rowi or P. Conradi. 



Cephalon This part of the body is closely similar to that of P. Rowi and 

 P. angustifrons. The border is moderately broad, slightly convex on its 

 proximal edge, becoming gently concave outwardly as in P. Roici, but pro- 

 duced into shorter cheek-spines. The cheek is elevated and distinctly 

 ridged at about half the distance from the border to the base of the eye, and 

 is broadly flattened on the upper surface. 



The glabella has much the same proportions as in P. angustifrons, and 

 shows indications of three pairs of lateral glabellar furrows. The occipital 

 ring bears a central tubercle, which is situated on the upper surface as in 

 P. angustifrans, and not on the posterior margin as in P. Rowi. The basal 

 lobes in the occipital furrow are larger, but not so distinctly defined, and 

 the eye is smaller than in P. Rowi. 



The Thorax bears no feature of distinctive value except the general smooth- 

 ness of the test, and the rounded posterior margins of the axial segments. 



