NO. 24 PTARMIGANIA STRATA RESSER 2g 



more than half the width of the glabella, and are peculiar in that they 

 are sunken below the dorsal furrow and eye band. The slightly 

 upturned eye band is gently curved in the forward three-fourths and 

 more sharply in the latter fourth. The brim is depressed next to the 

 glabella and at the lateral angles in an irregular manner and is covered 

 by coarse radiating anastomosing lines. The associated pygidium is 

 also flat, with the axis standing above the pleural lobes. Like the 

 fixigenes the pleural platforms are depressed below both the axis 

 and.the outer segment which forms a rim. The first segment extends 

 into a spine. 



The depression of the brim in front of the glabella and a similar 

 downturning of the rear margins of the pygidial pleural lobes serve 

 to distinguish this species from its associates. 



Locality 54s. 



Holotype and paratypes. — U.S.N.M. Nos. 98497a-c. 



PROZACANTHOIDES OPTATUS, n. sp. 



Plate 3, figs. 24-30 



This is the commonest species of Prosacantlioidcs at the locality. 

 It is represented by the best-preserved material and, moreover, has 

 about average features for the group of species. 



The glabella is parallel-sided, with the rear pair of furrows rather 

 deeply impressed and the others represented by faint impressions. 

 The occipital furrow is deep and the rings bear a spine, as well as two 

 furrows parallel to the rear pair of glabellar furrows. Eyes are large, 

 with their greatest curvature toward the rear, the palpebral lobes 

 attaining their greatest width opposite the rear pair of glabellar fur- 

 rows. At their widest point the palpebral lobes exceed half the 

 glabellar width. Brim rather narrow ; outline of the front margin of 

 cranidium straighter than in most species. The posterolateral limbs 

 end in intragenal spines. 



Libragenes, attached to the holotype, are about as wide as the pal- 

 pebral lobes, with long, slender, genal spines, which are slightly ad- 

 vanced. The strong rim is heavily striated and the ocular platforms 

 are covered with a network of heavy anastomosing lines. 



The pygidium assigned to the species is well fused, with a rather 

 strongly tapered axis. Pleural segments are not entirely obliterated. 

 The first segment extends into rather long, stout spines, and a second 

 pair into small spines. 



Locality 54s. 



Holotype and paratypes.— -U.S.N.M. Nos. 98498a, a'-2. 



