24 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 95 



suture rather strongly divergent anterior to the eyes. Eyes large, 

 extending forward from the occipital furrow. Brim concave, with a 

 narrow rim sometimes demarcated. 



Libragenes, hypostoma and thorax unknown. 



Pygidium with a prominent axis, rather wide and highly arched, 

 terminated bluntly or with a postaxial ridge. Pleural lobes flat, pleura 

 turning sharply backward and ending in blunt spines ; usually well 

 fused but with the pleural grooves showing. 



Compared with Zacanthoides, Prosacanthoides is constructed on 

 a similar plan but the glabella expands forward and the pygidial axis 

 does not take up as much of the total area. In addition the pleura 

 are less fused, remaining more like those of an ordinary trilobite. 



Genotype. — Olenoides stissingensis Dwight. 



Numerous species occur in the Lower Cambrian of the Appa- 

 lachians. 



Prozacanthoides stissingensis (Dwight) 



Olenoides stissingensis Dwight, Amer. Journ. Sci., 3d ser., vol. 38, p. 147, 

 pi. 6, figs. 9-15, 1889; Vassar Bros. Inst., vol. 5, p. 105, pi., figs. 9-15, 1890. 



Lower Cambrian ; Stissing, Dutchess County, New York. 

 Coty pes.— U.S.N. M. no. 18365. 



Prozacanthoides charilla (Wolcott) 



Zacanthoides charilla Walcott (part), Smithsonian Misc. Coll., vol. 67, no. 2, 

 p. 40, pi. 6, fig. 9a, 1917 (not fig. g— Clavaspidella sylla). 



Middle Cambrian, Chetang; (loc. 61 o) Chetang Cliffs, 7 miles 

 northeast of Robson Peak, Alberta. 

 Holotype.—U. S.'N.M. no. 63753. 



PSALASPIS, n. gen. 



Diagnosis. — Peculiar trilobite of about average size. Strongly con- 

 vex longitudinally and including the libragenes, also in the opposite 

 direction. Glabella tapered, a little more than half the length of the 

 head ; conforming in convexity to the cranidium and only outlined 

 by the rather weak dorsal furrow; weak glabellar furrows present; 

 glabella keeled. Brim single, convex and turned downward. Fixigenes 

 narrow. Eyes small, situated behind the middle of the head. 



Libragenes evenly and highly convex, without rim and with a weak 

 occipital furrow, extended into very long recurved genal spines. 



Genotype. — Conocephalites patersoni Hall. 



Name. — i/'aAis = arch ; ao-7rts = shield. 



