90 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 148 



Anterior outline without definite geniculation. Border and doublure 

 very narrow throughout. 



Length of largest of hundreds of cranidia observed, 7 mm. Length 

 of largest pygidium 2.5 mm., width 7.5 mm. 



Discussion. — The cranidia may not be easy to distinguish from 

 immature examples of some of the larger species, but the combination 

 of cranidium and pygidium characterizes the species as definitely dis- 

 tinct from all others. The cranidium is extremely similar to that of 

 A. inermis, the distinguishing features being pointed out in the de- 

 scription of that species. The pygidium instead is very much like 

 A. walcotti and A. hridgei. 



Occurrence. — Lower part of the Aphelaspis zone, above the beds 

 with A. lata and below those carrying A. walcotti. Type locality is 

 cnq/17. Hurricane Hollow. Also in collections cnq/14, Shields Ridge, 

 cnq/15. Three Springs, and cnpV20, Washburn. 



Types.— Ro\oiy^&: U.S.N.M. 144665. Paratypes: U.S.N.M. 

 144666-8. 



APHELASPIS INERMIS Rasetti, new species 



Plate 19, figures 8-17 



Available material. — Numerous cranidia and free cheeks, and a few 

 tentatively assigned pygidia. 



Description. — Glabella of average shape and convexity; occipital 

 furrow shallow ; occipital ring bearing a node, lacking spine. Frontal 

 area averaging slightly less than half the glabellar length. Preglabellar 

 field somewhat convex longitudinally especially on midline. Border 

 defined by shallow furrow and change in slope, slightly convex, rather 

 narrow for the genus. Anterior section of facial suture moderately 

 divergent, straight to border furrow. Palpebral area slightly upsloping, 

 about 0.3 times the glabellar width. Palpebral lobes set off by very 

 shallow furrow, somewhat elevated, averaging 0.3 times the glabellar 

 length and somewhat less than distance from posterior margin. Width 

 (tr.) of posterior area equal to width of occipital ring. Free cheek 

 with slightly convex border defined by shallow furrow. Genal spine 

 oval in cross section, rather thick and long. 



Pygidia associated with the cranidia in more than one collection are 

 transversely subelliptical, about 2.5 times as wide as long. Axis very 

 prominent, equally long and wide, rounded posteriorly, with 1 distinct 

 ring. Pleural lobes with 2 pairs of furrows and indistinct interpleural 

 grooves, all ending in flat border which is wider laterally than medially. 



Surface of test pitted in furrows of cranidium and free cheek, but 

 not as coarsely as in ^. arsoides. Length of unusually large cranidium 

 9 mm. Most of the specimens do not exceed 6 mm. 



