NO. 3 CAMBRIAN TRILOBITES 1/5 



A. stenometopus (pi. 24, fig. i), or broad as in A. amcricanus (pi. 24, 

 fig. 2). Acrocephalites hayncsi (pi. 24, fig. 4) has a strong occipital 

 spine. 



Thorax with 17 to 25 segments of the type of those occurring in 

 Ptychoparia striata (Emmrich), narrow, and with an almost straight 

 pleural furrow that begins to narrow at the genal angle of the 

 segment. 



Pygidium small and with three or four narrow transverse rings 

 that extend out on the pleural lobes as rather faint lines. 



The surface of all known species of the genus is more or less 

 strongly tuberculated. 



Stratigraphic range. — The type species occurs in the Agnostus 

 Icevigatus zone of the Middle Cambrian. The American species 

 occur as follows : 



Acrocephalites vulcanus, Lower Cambrian. 



Acrocephalites americaniis, Middle Cambrian. 



Acrocephalites aoris. Middle Cambrian. 



Acrocephalites insignis, Middle Cambrian. 



Acrocephalites ? majus. Middle Cambrian. 



Acrocephalites multisegnicntus, Middle Cambrian. 



Acrocephalites tutus. Middle Cambrian. 



Acrocephalites aster, Upper Cambrian. 



Acrocephalites haynesi. Upper Cambrian. 



Acrocephalites ? glomeratus. Upper Cambrian. 



Geographic distribution. — Sweden, eastern United States in the 

 states of Georgia, Alabama, and Vermont; western United States 

 or Cordilleran area ; in the Grand Canyon, Arizona ; in Utah, and 

 Montana. 



Observations. — Wallerius illustrates with rather indifferent figures 

 the cranidium and a free cheek oi A. stenometopus. Through the 

 kindness of Dr. Joh. Chr. Moberg I have had the opportunity of 

 having an enlarged photograph made of the type specimen now in 

 the collection of the University of Lund (pi. 24, fig. i). The cra- 

 nidium of A. aster (pi. 26, figs. 9, ga-c) is closely related to that of 

 A. stenometopus, but the nearest complete American species is A. 

 americaniis (pi. 24, figs. 2 and 3), which is fortunately represented 

 by nearly entire specimens. The thorax has 27 segments and a small 

 pygidium. The free cheek has a postero-lateral spine, in this respect 

 being similar to the free cheek of A. stenometopus as illustrated by 

 Wallerius. The thorax of ^. multisegmentus has 25 or more seg- 

 ments (pi. 24, fig. 5a). 



