NO. 3 CAMBRIAN TRILOBITES 183 



and marked by two or three pairs of short lateral furrows. Free 

 cheeks of medium size. 



Thorax with 17 to 19 narrow segments ; axial lobe narrow ; pleural 

 lobes broad and with well-defined furrows that extend from the 

 dorsal furrow outward to the backward-bending genal angle, where 

 they narrow and disappear on the smooth slope of the outer section 

 of the segment. 



Pygidium small; axial lobe rather prominent and divided into 

 about three rings by shallow, transverse furrows ; pleural lobes 

 small and marked by one or two transverse furrows. 



Surface slightly roughened by shallow pits when enlarged by a 

 strong lens. 



Genotype. — ConocepJialitcs stihcoronatus Hall and Whitfield. 



Stratigraphic range. — The genotype occurs in the lower portion 

 of the Middle Cambrian. Alokistocare althea, A. labrosum, A. lin- 

 narssoni, A. pomona, and A. prospectense occur in the Middle Cam- 

 brian, and A. althea in the Upper Cambrian. 



Geographic distribution. — Species of the genus occur in northern 

 Arizona, central Nevada, western and northern Utah, and northern 

 central Montana. It appears to have been limited to the interior 

 seas of the western portion of North America. 



Observations. — Dr. Lorenz compares the genus with his Macro- 

 toxus and assigns to it A. subcoronatnm (Hall and Whitfield) as 

 the genotype, stating that it has long, bow-shaped eyes, punctate 

 shell, and strong dorsal furrows about the glabella. He gained his 

 impression of the long eyes (palpebral lobes) from Hall and Whit- 

 field's illustration, but this was somewhat in error, as the palpebral 

 lobes are not over one-sixth the length of the cranidium on the type 

 specimen of the species now in the United States National Museum 

 collections (pi. 25, fig. 2). Lorenz did not compare it with the 

 closely related genus Acrocephalites, owing probably to the frag- 

 mentary specimens and incomplete illustrations of the latter genus. 

 Comparison between the two genera is made in this paper under 

 observations on Acrocephalites. 



Alokistocare althea (pi. 25, fig. 4a) has 19 thoracic segments, and 

 A. pomona (pi. 25, fig. 6), 18 thoracic segments. The segments 

 are of the same type as those of Ptychoparia striata'^ and of Acro- 

 cephalites americanus (pi. 24, fig. 3a) . The upward-curving frontal 

 rim or border of the type species (pi. 25, fig. 2) occurs in most of 



^Research in China, Carnegie Inst, of Washington, Vol. 3, Pub. No. 54, 

 1913, pi. 2, fig. 4. 



