NO. 3 UPPER CAMBRIAN TRILOBITE FAUNAS — RASETTI 31 



brevilobus. Further members of the faunule are Blountia bristolensis 

 and Glaphyraspis parva. Blountia bristolensis was not found in the 

 Crepicephalus zone but is there represented by the very similar 

 Blountia montanensis. Glaphyraspis was not found in Tennessee below 

 the Aphelaspis zone. However, the author collected cranidia attributed 

 to G. parva in a late Crepicephalus zone faunule from northeastern 

 Virginia (Rasetti, 1961). 



In the Hurricane Hollow section, also, an interval of a few feet 

 separates the uppermost Crepicephalus zone faunule from the earliest 

 Aphelaspis zone faunule in a uniform succession of massive limestone 

 beds. Here, however, the only remnant of the Crepicephalus fauna is 

 the genus Blountia, represented again by B. bristolensis. It is asso- 

 ciated with Aphelaspis transversa and Cheilocephalus brevilobus. 



The transition between the two faunizones is excellently shown in 

 the Three Springs section. Here the rock at this level is mostly shale 

 with thin fossiliferous limestone beds and lenses. The earliest Aphel- 

 aspis zone faunule (loc. cno/15) is essentially the same as at Russell 

 Gap, holding in great abundance Aphelaspis buttsi and Glaphyraspis 

 parva, with rare specimens of Coosella perplexa. 



At all these localities, Coosella is absent from higher beds, while 

 Blountia and Glaphyraspis continue in association with different species 

 of Aphelaspis. In this portion of the section faunal changes may occur 

 within a few feet of beds, and very accurate determinations of the rela- 

 tive positions of beds and lenses are required to avoid mixing forms 

 that do not occur together. In the field every single lens was labeled 

 separately and its stratigraphic position carefully recorded. In the 

 Russell Gap and Three Springs sections, a characteristic faunule (Iocs. 

 cnp/14, cnp/15) including innumerable remains of Aphelaspis lata, 

 a close relative of A. buttsi, occurs a few feet above the faunule de- 

 scribed above. Associated species are Blountia bristolensis, Cheiloce- 

 phalus brevilobus, and Glaphyraspis ornata. This faunule is well 

 represented also in the Washburn section (loc. cnp/20) . 



In the Three Springs section, in a thin bed 1 foot higher, Aphelaspis 

 walcotti appears in association with A. lata. This is an unusually early 

 occurrence of that species which is more common in higher strata. 

 Still 6 inches higher, another species of Aphelaspsis, A. minor, makes 

 its appearance in the Three Springs section and is also common in the 

 equivalent position in the Russell Gap and Hurricane Hollow sections 

 (Iocs, cnq/15, cnq/14, cnq/17). Associated forms, as in the under- 

 lying faunule, are Blountia bristolensis, Cheilocephalus brevilobus, and 

 Glaphyraspis ornata. 



The next higher faunule, known from a number of sections, is char- 

 acterized by Aphelaspis walcotti, the t3^e species of the genus. The 



