NO. 5 CAMBRIAN TRILOBITES 327 



granulation is formed on the lines of the fine ridges very much as 

 they occur on Corynexochus hubaris. 



The associated pygidium is more transverse than that referred to 

 C. (Bonnia) parvulus and also closely granulated. 



The largest cranidium has a length of 7 mm. 



Formation and locality. — Lower Cambrian: (20) Limestone 

 boulders in conglomerate ; on shore at east entrance to harbor at 

 Bic, Rimouski County, Quebec, Canada. 



CORYNEXOCHUS (BONNIA) FIELDENSIS (Walcott) 



Plate 57, figs. 4. 40-6 



Protypus Heldensis Walcott, 1908, Smithsonian Misc. Coll., Vol. 53, p. 215. 

 (Listed.) 



Corynexochus (Bonnia) Heldensis differs from C. (Bonnia) par- 

 vulus (Billings) in details of cranidium and pygidium. The glabella 

 is proportionally more elongate in specimens embedded in the same 

 character of limestone ; the axial lobe of the associated pygidium is 

 less elevated posteriorly. 



The differences are slight but persistent, and if occurring in speci- 

 mens from the same locality and layer of rock would probably receive 

 little attention. With the localities 2,000 miles (3,200 km.) distant 

 from each other, they are given more weight. 



The associated pygidium has the same kind of spines at the outer 

 end of the frontal margin, and the rings of the axial lobe and their 

 extension on the pleural lobes are the same except that those of 

 C. (B.) parvulus are more clearly defined. 



The occipital ring has a small median spine on the posterior margin 

 very similar to that of C. (B.) parvulus. 



Surface of test punctate and only faintly marked by fine, irregular, 

 inosculating ridges. 



The average length of the cranidium is about 9 mm. 

 The separate cranidia and pygidia occur in great numbers in the 

 limestone of the Mount Whyte formation in association with Meso- 

 nacis gilberti and O. canadensis. On Mount Bos worth (locality 

 35h) the fauna includes : 



Nisusia festinata (Billings) 



Scenella varians Walcott 



Hyolithcllus 



Ptychoparia 



Agraulos 



Olenellus canadensis Walcott 



Mesonacis gilberti (Meek) 



Corynexochus {Bonnia) Heldensis Walcott 



