NO. 5 CAMBRIAN TRILOBITES 349 



brian, in the long cliff about 2.5 miles (4 km.) east-southeast of 

 Marjum Pass, House Range, Millard County, Utah. 



POLIELLA, new subgenus 



The species B. {Poliella) powersi, B. (Poliella) anteros, B. {Poli- 

 ella) occidentalis, B. {Poliella) primus, B. (Poliella) caranus, B. 

 {Poliella) sylla, B. {Poliella) halus, and B. {Poliella) probus all sug- 

 gest by their small and different pygidia a subgeneric distinction from 

 the typical species of Bathyuriscus, B. haydeni, and for them I propose 

 the subgenus Poliella. 



The range in the number of thoracic segments is from 7 {B. 

 {Poliella) caranus (pi. 46, fig. 8)) to 11 {B. {Poliella) powersi (pi. 

 46, fig. i)). Bathyuriscus {Poliella) pozversi, of the Middle Cam- 

 brian, with its 1 1 segments and small pygidium, is a primitive form of 

 Poliella, while B. {Poliella) primus, of the Lower Cambrian, has a 

 more highly developed Dolichomet opus-like cephalon, eight thoracic 

 segments, and a very well developed though small pygidium. 



Genotype. — Bathyuriscus {Poliella) anteros Walcott. 



Observations. — Most of the species of Poliella are small. Of the 

 two larger species, B. {Poliella) primus has a length of 27 mm., and 

 B. {Poliella) balus about 30 mm. 



The stratigraphic range and geographic distribution are given 

 under the genus Bathyuriscus (p. 330). 



BATHYURISCUS (POLIELLA) ANTEROS, new species 



Plate 46, fig. 5 



This neat species has a relatively large cephalon, nine thoracic 

 segments and a small pygidium. Of the eight entire dorsal shields 

 found the largest has a length of 18 mm. It is similar in general 

 character to B. {Poliella) occidentalis (pi. 46, fig. 3), but differs in 

 having a larger palpebral lobe and a smaller pygidium in proportion 

 to the thorax. How much this may be owing to the imperfection 

 of the specimen of B. (Poliella) occidentalis, it is difficult to deter- 

 mine. The latter occurs in a hard, very fine-grained arenaceous shale, 

 and B. (Poliella) anteros in a moderately compact argillaceous shale 

 in which the specimens retain much of their original convexity. 



Bathyuriscus (Poliella) anteros differs from B. haydeni in many 

 details of the cranidium, thorax, and especially the pygidium. A 

 comparison with B. (Poliella) primus will be found under that 

 species. 

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