NO. 3 UPPER CAMBRIAN TRILOBITE FAUNAS — RASETTI 93 



posterior border furrow with shallow extension on proximal portion 

 of genal spine. 



Associated pygidium with large axis, wider than pleural lobes, ele- 

 vated, rounded at the extremity, showing 3 poorly defined rings plus 

 a terminal section. Anterior outline of pleural lobes showing genicula- 

 tion not far from axial furrow, then bending backward rather sharply ; 

 posterior margin with maximum curvature on midline. One pair of 

 pleural furrows well impressed, two other pairs shallow and rather 

 indistinct. Border narrow, poorly defined by border furrow. 



Surface of cranidium and free cheeks almost entirely covered with 

 fine, dense puncta. Surface of pygidium also punctate. Length of 

 largest cranidium 8 mm. Length of pygidium 2.1 mm., width 3.7 mm. 



Discussion. — The cranidium of this species would be distinctive 

 even without the unique feature of the punctate surface because of 

 the deep pits in the axial furrow, the roll in front of the glabella, and 

 the elevated palpebral lobes. All these features tend to give the species 

 an aspect approaching Dytremacephalus angulatus. The pygidium is 

 also distinctive in shape, having a proportionately larger axis than 

 other species of Aphelaspis. 



Occurrence. — Uppermost beds of the Aphelaspis zone, in associa- 

 tion with Aphelaspis tarda. The type locality is cnw/14. Shields Ridge, 

 but the species is less rare at locality cnw/20, Washburn. 



Ty/'^.y.— Holotype : U.S.N.M. 144673. Paratypes: U.S.N.M. 

 14467^5. 



APHELASPIS ARSES (Walcott) 



Plate 13, figures 16-23 



Saratogia arses Walcott, 1916a, p. 196, pi. 35, figs. 4-4b. 

 Clevelandella arses (Walcott) Resser, 1938a, p. 69, pi. 13, fig. 22. 



Available material. — The hypodigm consists exclusively of the holo- 

 type, a good cranidium in limestone. Collections by the author sup- 

 plied numerous cranidia and free cheeks and a few pygidia. 



Description. — Glabella of average shape and convexity. Occipital 

 furrow well defined throughout, deeper than in most species of the 

 genus. Occipital ring bearing a small node and, in addition, a long, 

 slender, somewhat upturned spine. Frontal area averaging half the 

 length of glabella (exclusive of spine). Preglabellar field slightly con- 

 vex longitudinally. Border narrow, defined by shallow furrow and 

 change in slope, in most specimens definitely convex. Anterior sections 

 of facial suture quite straight from palpebral lobe to border furrow. 

 Palpebral area slightly convex, horizontal to slightly upsloping, aver- 

 aging 0.3 times the glabellar width. Ocular ridges broad but distinct, 

 slanted backward. Palpebral lobes set off by distinct furrow on upper 



