NO. 3 UPPER CAMBRIAN TRILOBITE FAUNAS — RASETTI 81 



more than half the length of preglabellar field. Palpebral area 0.4 

 times as wide as glabella, approximately horizontal; ocular ridges 

 faint, with transverse course. Sagittal length of palpebral lobe 0.3 

 times the glabellar length, and about 0.6 times the distance from pos- 

 terior end of palpebral lobe to posterior margin. Width (tr.) of 

 posterior area 1.1 times the width of occipital ring. 



Free cheek with relatively convex ocular platform, and wide, flat 

 border upturned with respect to platform. Genal spine broad at base, 

 rather rapidly tapered, flat on upper side, in most specimens somewhat 

 curving upward. Depression at end of posterior border furrow deeper 

 than in most species of the genus. 



Pygidium definitely identified from collections where the species 

 occurs alone. Pygidium about 3 times as wide as long ; anterior margin 

 fairly straight, anterior angles narrowly rounded. Axis tapered, show- 

 ing 2 and sometimes 3 rings plus a terminal section. Two or three 

 pairs of broad, shallow pleural furrows usually visible; some speci- 

 mens also show a trace of interpleural grooves. 



Length of largest cranidia 16 mm. Length of largest pygidium 5 

 mm., width 15 mm. 



Discussion. — The species is well distinguished, at least statistically, 

 by the low glabella, strongly convex preglabellar field, anterior posi- 

 tion of the eyes, and considerable width (tr.) of the posterior area. 

 However, single cranidia, especially if incompletely preserved, may 

 be confused with such species as A. walcotti, A. quadrata, and A. 

 tarda. The pygidium resembles those of A. walcotti and A. hridgei. 



Occurrence. — The type locality is U.S.N.M, 120 on Shields Ridge ; 

 beds holding this species are not now exposed at that locality. The 

 stratigraphic position of the species is well established by its occur- 

 rence in the author's collections cns/4, cns/15, cns/16, cnsVlS, 

 cnr/20, and cnrV20. 



Types. — Holotype and paratypes: U.S.N.M, 94929. Plesiotypes: 

 U.S.N.M. 144643-5. 



APHELASPIS PALMERI Rasetti, new species 



Plate 14, figures 13-19 



Available material. — Several cranidia, free cheeks, hypostomes, and 

 pygidia. 



Description. — Glabella of average shape and convexity; occipital 

 ring bearing a small node. Preglabellar field convex longitudinally, 

 steeply downsloping in anterior portion, forming sharp angle with 

 horizontal, slightly convex border. Preglabellar field about one and 

 one-half times as long (sag.) as border; entire frontal area about 



