KO. 5 CAMBRIAN TRILOBITES RESSER 5 



dently based on other than the type species, which is correct in most 

 essential points. Furthermore, it now appears that Ainecephalus was 

 not well founded and is congeneric with A. subcoronatum. The rela- 

 tionship between A. siibcoronatmn and A. piochensis is apparent in 

 the cranidium, and if the pygidium mentioned above represents A. 

 sitbcoronatuni, this part also conforms. In addition several entire in- 

 dividuals belonging to undescribed species prove this relationship. 

 A new generic diagnosis based on the enlarged group is given below. 



Diagnosis. — Entire many-segmented trilobite tapering from a wide 

 cephalon to a small pygidium. 



Cephalon semicircular, and usually with considerable convexity. 

 Facial suture diverges only slightly in front of the eyes and is intra- 

 marginal for perhaps one-third the distance to the center. Behind 

 the eyes it diverges rapidly, forming short, blunt posterolateral limbs. 

 Glabella marked off by well-defined dorsal furrow ; tapers slightly 

 and has three or four usually short glabellar furrows ; length usually 

 slightly more than half the length of the cranidium. Occipital furrow 

 developed ; neck ring thickened. Brim wide ; rim usually defined but 

 sometimes by only a faint furrow ; preglabellar area equal to or 

 wider than the rim ; and in common with many wide-brimmed trilo- 

 bites usually has a more or less well developed median boss ; brim 

 striated vertically, anterior to the eye lines. Fixed cheeks wide, with 

 large, strongly bowed palpebral lobes. Eye ridges usually strong ; eyes 

 small, situated about the middle of the glabella. Free cheeks fairly 

 large, concave toward the margin and with flat, sometimes concave 

 genal spines. 



Thorax with approximately 20 segments, which are directed rather 

 straight out, bending downward at the fulcrum and ending bluntly. 



Pygidium small, not exceeding in width the diameter of the glabella 

 at the occipital furrow. Axis usually highly arched, as are also the 

 pleural portions. Pleura fused ; rim usually not demarcated. 



Surface striated vertically on the brim ; some species are pustulose 

 or granulose, sometimes with both a fine and a coarse set. 



Genotype. — Conocephalitcs subcoronatiis Hall and Whitfield. 



Range. — Chiefly in the ]\Iiddle Cambrian, but also late Lower 

 Cambrian. 



Species formerly referred to Alokistocare: 



A. lahrosiim = Bolaspis A. prospectense = Eldorad'n 



A. linnarssoni = Eldoradia A. ticida = Bolaspis 



