NO. 24 PTARMIGANIA STRATA RESSER 7)7 



section the cranidium is convex. Longitudinally it is considerably 

 more so, with a rather even curvature throughout. The palpebral 

 lobes are just half the width of the glabella, and the eyes are of 

 normal size and normal curvature. The palpebral furrow is shallow, 

 but the eye band is fairly well defined. The brim is very narrow, 

 expanding to meet the moderate flanges at the anterior angles. The 

 pygidia assigned to the species has a rather high axis, abruptly termi- 

 nated in the rear. The marginal spines increase rearward until the rear 

 pair is quite long. Owing to the convexity and the granulations on the 

 spines, there is some question regarding assignment of the pygidium. 

 The cranidial surface seems to be nearly smooth. 



Locality 54s. 



Holotype and paratopes. — U.S.N.M. Nos. 985i3a-c. 



PTARMIGANIA 3 RAYMOND, 1928 



Ptarmigania is represented by many species. Separation of 

 Ptarmigania and Dolichometopsis can be made only when pygidia are 

 available. . In a species such as P. exigua the pygidial border has one 

 definite and three blunt spines, the latter little more than irregularities 

 of the edge. In most species the margin has been smoothed out much 

 more, so that there is scarcely anything more than a slight production 

 of the anterior angles to represent the spines. Ptarmigania also has 

 a large axial spine on the first pygidial segment. Most of the species 

 are granulated. 



The cranidium of Ptarmigania resembles that of Clavaspidella, but 

 the pygidium is differently constructed. Aside from the lack of an 

 axial spine, Clavaspidella typically has a rounded triangular or semi- 

 circular tail, while Ptarmigania has a transverse pygidium always 

 wider than long. 



PTARMIGANIA AURITA, n. sp. 



Plate 3, figs. 35, 36 



A single small cranidium is particularly marked by its nearly smooth 

 surface and shallow glabellar furrows. The glabella expands forward 

 from the first pair of glabellar furrows. The usual furrows are 

 present but shallow, and the occipital spine evidently was large. The 

 fixigenes, which are confined to the palpebral lobes, are about three- 

 fourths the average glabellar width. The cranidium has considerable 

 convexity longitudinally, and in cross section the glabella stands com- 



3 Ptarmigania was erroneously recorded in the bibliographic records as 

 Ptarmingia. This error of spelling inadvertantly got into the literature. 



