NO. 3 UPPER CAMBRIAN TRILOBITE FAUNAS — RASETTI 33 



An approximate equivalent of the last-mentioned assemblage is the 

 one collected from Monroe County (U.S.G.S. collection 2970) with 

 Aphelaspidella macropyge, Aphelaspis arses, A. palmeri, Cheiloceph- 

 alus, sp., Dunderbergia longifrons, Dytremacephalus strictus, and 

 Paraphelaspis vigilans. 



In Jefferson County, lenses at the previously mentioned locality 

 cns/4 also yield Aphelaspis arses and A. inermis, both also present in 

 collection cns/2, accompanied by Cheilocephalus sp. and Pseudagnostus 

 communis. 



Above these faunules appears a widespread assemblage characterized 

 in all sections where it is known by innumerable examples of Aphel- 

 aspis tumifrons. It was collected from Big Creek (cns/1, cnt/1), Lost 

 Creek (cnt/4), Shields Ridge (cns/2), Three Springs (cnt/15, 

 cntVlS), Smith Hollow (Oder's coll. No. 14), Washburn (cnt/20, 

 cnt720), River Ridge (cnt/21), and Purchase Ridge, Va. (cnt/7). 

 Here should be mentioned the exceptional occurrence at Lost Creek 

 in the collection cnt/4 of very rare specimens of Dytremacephalus 

 angulatus, a species that becomes common in strata of the upper 

 Aphelaspis zone. Normal associates of Aphelaspis tumifrons are in- 

 stead Aphelaspis arsoides, Cheilocephalus sp., and Pseudagnostus 

 communis. 



The beds above the Aphelaspis tumifrons faunule and up to the top 

 of the fossiliferous sequence, i.e., to the top of the Nolichucky forma- 

 tion (or Maynardville limestone), shall be assigned to the upper 

 Aphelaspis zone. One faunule seems to occupy this interval, covering 

 in the Big Creek section about 70 feet of strata, and the characteristic 

 species are Aphelaspis tarda and Dytremacephalus angulatus. Less 

 frequent and widespread are Aphelaspis punctata, Cheilocephalus 

 hrachyops, Dunderbergia tennesseensis, and the rare Dytremacephalus 

 sulcifrons. This Aphelaspis tarda faunule was collected at Big Creek 

 (cnu/1, cnv/1, cnw/1, cnx/1). Purchase Ridge (cnu/7, cnv/7, 

 cnvV7), Russell Gap (cnw/14). Three Springs (cnu/15, cnv/15), 

 Smith Hollow (Oder's coll. No. 14A), Washburn (cnw/20, cnx/20), 

 and River Ridge (cnu/21, cnv/21 ) . 



In Tennessee all the higher fossiliferous beds of the Nolichucky, up 

 to the top of the formation, have been assigned to the Aphelaspis zone, 

 since the faunules are very homogeneous, being dominated by species 

 of Aphelaspis. However, the younger of these faunules may be equiva- 

 lent to faunules attributed by Palmer to post- Aphelaspis zones in the 

 western sections (see later discussion). 



It seems likely that the vertical distribution of genera and species 

 described above does not mean that each species only lived for the short 

 time span indicated by the thickness of beds through which it was 



