78 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 148 



it may be distinguished, at least statistically, by the slightly down- 

 sloping palpebral area, flat rather than concave border of the free 

 cheeks, and more deeply furrowed pygidium. In some respects the 

 species is transitional between A. lata and A. walcotti. 



Occurrence. — U.S.G.S. collection 2804, from N. slope of Shields 

 Ridge on New Market-Piedmont road, in upper part of lower lime- 

 stone unit of the Nolichucky. The association with Blountia bristolen- 

 sis and Glaphyraspis ornata shows that the species belongs to the 

 lower portion of the Aphelaspis zone. The author was unable to 

 collect fossils from this portion of the zone at the locality. The nearby 

 locality at Russell Gap yielded fossils of the basal Aphelaspis zone, 

 including, in ascending order, Aphelaspis lata and A. minor. The 

 present species presumably occurs in higher beds, but lower than 

 those which yielded Aphelaspis camiro, A. laxa, and A. quadrata at 

 their type locality, U.S.N.M. 120, which is also on the New Market- 

 Piedmont road. 



T3;/>?.y.— Holotype : U.S.N.M. 144635. Paratypes: U.S.N.M. 

 144636. 



APHELASPIS QUADRATA Resser 



Plate 18, figures 1-9 

 Aphelaspis quadrata Resser, 1938a, p. 59, pi. 13, figs. 16-17. 



Available material. — The holotype is a large, somewhat incomplete 

 cranidium. The collection from the type locality includes several 

 cranidia and pygidia, from which a clear picture of the specific char- 

 acters can be gathered. The species was collected by Dr. Oder and the 

 writer from the Three Springs, Washburn, and Smith Hollow sec- 

 tions. Free cheek and pygidium were unequivocally identified. 



Description. — Glabella of average shape and convexity, defined by 

 a well-impressed axial furrow. Preglabellar field downsloping, of 

 moderate and fairly uniform convexity. Border averaging two-thirds 

 of the sagittal length of preglabellar field, upturned and hence forming 

 a sharp angle with the preglabellar field, almost flat ; border furrow 

 uniformly curved. Frontal area on average 0.50 times as long as 

 glabella inclusive of occipital ring. Palpebral area slightly convex, 

 horizontal to slightly upsloping. Ocular ridges definitely slanted back- 

 ward. Length of palpebral lobe 0.25 times length of glabella plus 

 occipital ring, and 0.7 times distance from posterior end of palpebral 

 lobe to posterior margin. Anterior section of facial suture with average 

 divergence. Width (tr.) of posterior area equals width of occipital 

 ring. 



Free cheek with fairly convex ocular platform. Border flat, up- 

 turned. Genal spine relatively short, rapidly tapered. 



