NO. 3 UPPER CAMBRIAN TRILOBITE FAUNAS — RASETTI 85 



on outer surface on preglabellar field and ocular platform, well marked 

 on internal impression. Length of largest cranidium 21 mm. ; length 

 of largest pygidium 7 mm., width 14 mm. 



Discussion. — This is a large species, whose cranidia somewhat re- 

 semble A. camiro. They differ in the narrower and more elevated 

 anterior border, proportionately longer palpebral lobes, and lesser 

 width (tr.) of the posterior area. The free cheek and genal spine are 

 also very similar to that species. The pygidium is quite distinctive, 

 with a proportionately narrower axis and regularly oval rather than 

 subtrapezoidal outline. 



Unless careful attention is paid to the divergence of the anterior 

 sections of the facial suture, cranidia of Aphelaspis rohindata may be 

 confused with those of the associated species Aphelaspidella macro- 

 pyge. Even though there is some variability in the divergence of the 

 sutures in either species, usually well-preserved cranidia can be classi- 

 fied on this character alone. The pygidia are immediately distinguish- 

 able, although the pygidium of Aphelaspis rotundata, with its doublure 

 wider than in most species of the genus, approaches in shape the 

 pygidium of Aphelaspidella. 



Occurrence. — Medial portion of the Aphelaspis zone, in association 

 with Aphelaspis arses, Aphelaspidella macropyge, and Paraphelaspis 

 vigilans. The type locality is cns/20, Washburn. Also present in col- 

 lections cns/20a, Washburn, cnq'V4, Lost Creek, and ens'/ 15, cns'V 

 15, Three Springs. 



Tv/'^.y.— Holotype : U.S.N.M. 144652. Paratypes: U.S.N.M. 

 144653-4. 



APHELASPIS WASHBURNENSIS Rasetti, new species 



Plate 17, figures 15-23 



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



Description. — Glabella relatively small in proportion to cranidium, 

 of low convexity but defined by a fairly deep axial furrow. Frontal 

 area averaging 0.75 times the length of glabella plus occipital ring. 

 Preglabellar field tumid, strongly downsloping in anterior portion; 

 border well defined by sharp change in slope, about half as long (sag.) 

 as preglabellar field. Palpebral area somewhat upsloping, unusually 

 wide (somewhat more than half the glabellar width) ; ocular ridges 

 transverse ; palpebral lobes about 0.3 times the length of glabella plus 

 occipital ring; distance from posterior end of palpebral lobe to pos- 

 terior margin about equaling length of palpebral lobe. Anterior section 

 of facial suture diverging at average angle; anterior angles of era- 



