104 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 148 



The species is common in the basal beds of the Aphelaspis zone in 

 Tennessee. The largest cranidium observed has a length of 20 mm. 

 and a width between the tips of the posterior area of 40 mm. The 

 largest pygidium has a length of 21 mm. and a width of 34 mm. 



The free cheek has never been described. Fragments are common 

 in association with other parts of the exoskeleton, but it is difficult 

 to prepare good specimens. The free cheek has a concave border not 

 differentiated from the ocular platform by a furrow. The facial suture 

 cuts the posterior margin very close to the genal angle. This is ex- 

 tended into a short, flat, triangular genal spine. Hence the suture does 

 not have a proparian course, as some authors have conjectured. 



Occurrence. — The types are from an unspecified horizon in the 

 Nolichucky formation at U.S.N.M. locality 118a, near Greeneville, 

 Greene County. Collected by the author at localities cno/14, cnp/14, 

 cnq/14, cnp/17. 



Types.— Holotype: U.S.N.M. 62852. Paratypes: U.S.N.M. 

 62853^. Plesiotypes: U.S.N.M. 144707-8. 



CHEILOCEPHALUS BRACHYOPS Palmer 



Plate 17, figures 6-11 



Cheilocephalus brachyops Palmer, 1965, p. 105, pi. 1, figs. 12-15, 17. 



A species of Cheilocephalus that occurs in the upper Aphelaspis 

 zone fully agrees in all characters of cranidium and pygidium with the 

 species, described from the Dunderbergia zone in Nevada. 



Occurrence. — Collections cnx/1, Big Creek, and cnw/14, Shields 

 Ridge. 



T3>/>^5.— Plesiotypes: U.S.N.M. 144709-10. 



CHEILOCEPHALUS, species undetermined 



Plate 17, figures 12-14 



Rare specimens of Cheilocephalus that occur in the middle portion 

 of the Aphelaspis zone possess a frontal area short as in C. brachyops, 

 but flat and lacking the raised border of that species. The surface 

 shows indistinct ornamentation. The pygidium is like both C. brevi- 

 lobus and C. brachyops. A close comparison is made uncertain by the 

 fact that all the specimens in question are small and obviously imma- 

 ture. Hence it will be left undecided whether this form should be 

 assigned to a new species. 



Occurrence. — The figured specimens are from locality cnr/4. Lost 

 Creek. Also present in collections cns/4, cns/2, and U.S.G.S. 2970. 



Disposition of material. — Figured specimens: U.S.N.M. 144711. 



