310 



NORTH AMERICAN INDEX FOSSILS. 



large, forward projecting, compound lobes, while between these 

 and the neck furrow is a pair of occipital lobes. Genal spines 

 curved outward and backward. Pygidium with a thickened bor- 

 der; axis elevated; pleural segments two, each produced into a 

 backward curving spine. Siluric. 

 142. C. phlyctainodes (Green). (Fig. 162 1, &-^.) Siluric. 



Fig. 1621. a, Arctimirus occidenialis, pygidium, X Ys *> ^-^^ Corydocephalus 

 phlyctainodes : b, c, top and side view of spineless cranidium ; d, a spinose cranidium ; 

 <f, pygidium (all X /^) > /> ^» Dicranopeltis decipiens, cephalon and pygidium, X H \ 

 h, Acidaspis guinquespinosa, imperfect cranidium, X %• {^S^ ^^ter Waller ; /i, after 

 Van Ingen.) 



Side lobes of glabella acutely angular behind; median lobe with 

 a pair of spines and each lateral lobe with a single long spine. 

 Pygidium with posterior part of each grooved segment ridge-like 

 and continued into the spine. 



Niagaran of New York, Ohio, Indiana, Illinois and Arkansas. 



LV. Dicranopeltis Corda. 



Cephalon triangular in outline, tuberculate. First glabellar fur- 

 row curving back to the neck furrow and deep anteriorly. Ante- 

 rior lateral lobes relatively larger and posterior lateral and occipital 

 lobes relatively smaller than in Corydocephalus, while all the lateral 

 furrows except the anterior pair are placed more transversely and 

 the glabella is narrower posteriorly. Axis of pygidium with two 

 annulations; lateral lobes flattened, with three pairs of grooved 

 segments, each ending in a free point. Siluric. 



