NO. 5 CAMBRIAN TRILOBITES 333 



illustration was diagrammatic and did not suggest the closely allied 

 form now described as B. {Poliella) primus (pi. 46, fig. 6), which 

 occurs 2,150 feet lower in the Mt. Stephen section. 



The Lower Cambrian species Bathyuriscus (Poliella) primus has 

 a small compact pygidium similar in relative size to that of B. (Poli- 

 ella) pozversi, which is associated with the type species, B. haydeni, 

 which has a large pygidium. 



Comparison of Bathyuriscus with Other Genera. 



Zacanthoides.^ — The type species of Bathyuriscus, B. haydeni, has 

 a very distinctive cranidium characterized by (i) a narrow, convex 

 glabella that expands in front of the anterior pair of lateral furrows ; 

 (2) a pair of posterior, oblique lateral furrows that are united by a 

 transverse furrow, and (3) three pairs of short lateral furrows, the 

 anterior two of which extend obliquely forward. This combination 

 of characters is almost identical with that of the glabella of Zacan- 

 thoides spinosus Walcott." The cranidium of B. haydeni has also 

 a long palpebral lobe, narrow fixed cheek, short frontal limb much 

 like those of Z. spinosus, and the occipital spines on the thoracic 

 segments are of the same type in the two forms, but the pygidia of 

 the two genera are unHke and very distinctive. 



CorynexocJms. — It may be compared with the Lower and Middle 

 Cambrian genus Corynexochus," from which it differs in the form of 

 its glabella, pleural furrows of thoracic segments, and pygidium. 



Vanuxemella* — It differs from Vanuxemella in the same way as 

 from Coryncxochus, and Vanuxemella has but five thoracic segments. 



Dolichometopusf — It differs from this genus in having distinct 

 glabellar furrows, more numerous thoracic segments, and in the 

 presence of distinct furrows on the pleural lobes of the pygidium. 

 The two genera, however, closely approach each other in such species 

 as Dolichometopus f bessus (pi. 51, figs. 3, 30-/?) and Bathyuriscus 

 hantius (pi. 49, figs. 2, 2a-c). 



Genesis. — Bathyuriscus appears to have been derived from a 

 Lower Cambrian ancestor that also gave rise to the allied genera 

 Dolichometopus, Coryfiexochus and its subgenus Bonnia. 



* American Jour. Sci., Vol. 2>^, 1888, p. 165. Smithsonian Misc. Coll., Vol. 53, 

 igo8, p. 26. 



^ Canadian Alpine Jour., Vol. i, No. 2, 1908, pi. 4, fig. i. 

 ^ Pal. Scandinavica, Angelin, 1854, p. 59, pi. 2>2>< fig- 9- 



* Smithsonian Misc. Coll., 1916, Vol. 64, No. 3, p. 220. 

 ' Pal. Scandinavica, Angelin, 1854, p. 72. 



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