NO. 3 UPPER CAMBRIAN TRILOBITE FAUNAS — RASETTI 77 



The species is closest to A. bridgei, A. quadrata, and A. tarda. The 

 differences will be discussed in describing these species. 



Palmer (1954) assigned to Aphelaspis walcotti material from Texas 

 which seems to include excessive variation to represent a single spe- 

 cies. The Texas pygidia differ considerably from the Tennessee forms, 

 hence it appears doubtful that the species exists in Texas. Cranidia 

 from Wyoming illustrated by Shaw (1956) certainly do not belong 

 to the species. 



Occurrence. — The type locality is U.S.N.M. lOu, near Saltville, Va. 

 The type locality for A. simulans is U.S.N.M. 117d, near Washburn, 

 Grainger County. Collected by the author at localities cnq/4, cnr/15, 

 cnr/16, cnq/16, cnrV17, and cnq/20. 



Types. — Holotype and paratypes : U.S.N.M. 94923. Holotype and 

 paratypes of Aphelaspis simulans: U.S.N.M. 94925-6. Plesiotypes: 

 U.S.N.M. 144632-4. 



APHELASPIS BRIDGEI Rasetti, new species 



Plate 13, figures 1-7 



Available material. — Large numbers of cranidia and less numerous 

 free cheeks and pygidia well preserved in limestone. 



Description. — Glabella defined by a shallow axial furrow, of usual 

 shape. Occipital furrow shallow, occipital ring bearing a small node. 

 Frontal area about 0.55 times as long as glabella. Preglabellar field 

 somewhat convex longitudinally ; border sharply defined by border 

 furrow and change in slope, slightly convex, approximately horizon- 

 tal; sagittal length of border almost equaling preglabellar field. Pal- 

 pebral area slightly downsloping, 0.4 times as wide as glabella. Aver- 

 age exsagittal length of palpebral lobe 0.34 times length of glabella 

 plus occipital ring and 0.84 times distance from posterior end of 

 palpebral lobe to posterior cranidial margin. Ocular ridges faint, 

 somewhat slanted backward. Width (tr.) of posterior area 0.8 times 

 the width of the occipital ring. 



Free cheek with flat border defined by shallow border furrow ; genal 

 spine flat on upper side, of moderate length. 



Pygidium about 2.8 times as wide as long. Axis tapered, showing 

 2 or 3 well-defined rings and a terminal section. Anterior outline of 

 pleural region almost straight, without apparent geniculation. Anterior 

 angles rounded, posterior margin regularly curved. Three pairs of 

 pleural furrows very distinct ; interpleural grooves faint. Furrows and 

 grooves not extending to narrow, flat border. 



Surface of all parts of test smooth. Length of large cranidium 

 10 mm. Length of largest pygidium 4.3 mm., width 12 mm. 



Discussion. — This species is very close to A. walcotti, from which 



