NO. 3 UPPER CAMBRIAN TRILOBITE FAUNAS — RASETTI 101 



laspis, seems best referred to Dytremacephalus, although the palpebral 

 area is wider than in D. granulosus and the palpebral lobe larger and 

 more posterior in position. The frontal and palpebral areas are more 

 like D. laevis Palmer (1954). In Nevada, Palmer (1965) finds two 

 species of Dytremacephalus in the lower part of the Dunderhergia 

 zone. In view of the somewhat questionable assignment of the present 

 species to the genus, this fact should not be attributed much signifi- 

 cance for correlation. Dytremacephalus angulatus differs from all spe- 

 cies of Aphelaspis in the deep axial furrows, more posterior position 

 of the eyes, granulate surface, and shortness of the genal spine. 



One should also note the considerable similarity of the cranidia of 

 this trilobite to Acrocephalaspis fidus Ivshin (1956) from Kazakhstan, 

 where it occurs in association with Aphelaspis, and hence may be taken 

 to be approximately of the same age as the present species. Unfortu- 

 nately Ivshin's material includes only cranidia. Ivshin compared Acro- 

 cephalaspis with Acrocephalites, but, judging from the illustrations, 

 his new genus seems very close to Aphelaspis. It is also possible that 

 Aphelaspis and Acrocephalites are closely related. 



Occurrence. — Mainly characteristic of the uppermost portion of the 

 Aphelaspis zone in Tennessee, usually associated with Aphelaspis 

 tarda. The type locality is cnw/14, Shields Ridge. Also present in col- 

 lections cnw/1, cnx/1, cnv/15, and U.S.G.S. 2969. A single specimen 

 was found in the collection cnt/4, from somewhat lower beds here 

 assigned to the upper portion of the middle Aphelaspis zone. 



Types.— Kolotype: U.S.N.M. 144686. Paratypes: U.S.N.M. 

 144687-9. 



DYTREMACEPHALUS SULCIFRONS Rasetti, new species 



Plate 12, figures 23-25 



Available material. — ^Two cranidia from different localities. 



Description. — Cranidium as a whole and glabella with greater longi- 

 tudinal convexity than in preceding species. Glabella with 2 fairly deep 

 pairs of lateral furrows, a third pair very short and shallow, more 

 rounded anteriorly than in D. angulatus. Shallow portion of axial 

 furrow shorter than in preceding species. Palpebral area, palpebral 

 lobes, and course of facial sutures as in D. angulatus. Surface orna- 

 mentation of the same type. Length of cranidium 6 mm. 



Discussion. — The differences from D. angulatus were pointed out 

 in the description. This may be an extreme case of variation within 

 that species ; however, in the absence of intermediate forms, it is de- 

 scribed as a representative of an associated, rare species. It resembles 

 the type species of the genus. 



