300 



FRED J. PACK 



Zacanthoides grabaui, n. sp. 



(Plate III. Figs. 3, T,a, 3&) 



This species is known only by the head, free checks, and some 

 fragments of the thoracic segments with spines attached. Two of the 

 specimens (Fig. 3 b) were collected by Mr. Charles Of. 



General form of the head triangular; glabella elongate, a little more than 

 twice as long as broad; sides parallel; front broadly rounded; surface moderately 

 convex; slight ridge extending lengthwise at summit; three pairs of well-marked 

 glabellar furrows, the posterior pair pointing obliquely backward, the second pair 

 directly across, and the anterior pair slightly forward ; occipital furrow fairly well 

 marked, and occipital ring provided with a knob or spine; posterolateral limb 

 provided with short thick spine. 



Frontal margin expanded into broad triangular area, one of the apices point- 

 ing directly forward; rim on either side of anterior apex slightly concave back- 

 ward; triangular area, provided with well-pronounced frontal rim; area flat with 

 slight elevation near center; marked with stria radiating from front of glabella; 

 frontal rim marked with fine stria extending longitudinally. 



Fixed cheeks moderately broad inside on the eye-lobe, highly contracted just 

 beyond front of eye, and then expanded into triangular frontal margin. 



Free cheeks broad and flat, bordered anteriorly and laterally by heavy rim 

 extending backward into a slightly curved genal spine, which apparently does 

 not pass beyona the fifth thoracic segment. 



Eyes narrow and long, reaching from opposite anterior pair of glabellar 

 furrows to opposite occipital ring. 



Axial lobe apparently same width as glabella, and rather highly convex; first 

 pleural lobe extends through an abrupt angle into a short stout spine; in the 

 second the spine is longer and the angle less abrupt; in the third the angle 

 disappears, the lobe and spine forming a gentle curve. 



In some ways this form resembles Z. typicalis, but differs from it in 

 the general shape of the head, the frontal margin, and the genal spines. 

 Location: Half Moon Mine. 



PLATE I 



Fig. I. — Eocystites?? longidactylus, Walcott. 



I. View of specimen showing the sac-like stem and the lobed plates; twice natural 



size. Collection Columbia University Museum, No. 20001. 

 I a. An arm showing the arrangement of the covering-plates; twice natural size. 



Collection Columbia University Museum, No. 20002. 

 lb. Slightly concave plate showing the lobate arrangement at margin; four times 

 natural size. Collection Columbia University Museum, No. 20003. 



