84 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 148 



upsloping palpebral area, flat preglabellar field with a more or less 

 distinct preglabellar boss, and anterior position of the eyes. The 

 pygidium is unique in its relatively long and narrow shape and well- 

 rounded sides. Immature cranidia, however, are not always easily 

 distinguishable from those of associated species. 



Occurrence. — The type locality is U.S.N.M. 120, Shields Ridge 

 (see discussion of A. quadrata and A. laxa). Also collected by the 

 author at localities cns/4, cns/15, cns/16, cnr/20, and cnrV20. 



Types. — Holotype and paratypes: U.S.N.M. 61672. Plesiotypes: 

 U.S.N.M. 144648-51. 



APHELASPIS ROTUNDATA Rasetti, new species 



Plate 14, figures 1-12 



Available material. — Numerous cranidia, free cheeks, and pygidia, 

 and a few hypostomes. Most of the specimens lack the test. 



Description. — Cranidium with low relief. Glabella and occipital 

 ring without distinctive features. Preglabellar field slightly down- 

 sloping, with little convexity; border furrow better defined than in 

 most species; border elevated, somewhat convex. Total length (sag.) 

 of frontal area averaging 0.6 times the length of glabella plus occipital 

 ring; midlength (sag.) of border about 0.3 times the midlength of 

 preglabellar field. Palpebral area averaging somewhat less than half 

 the glabellar width, upsloping; palpebral lobe also upsloping, defined 

 by shallow furrow even on outer surface. Exsagittal length of pal- 

 pebral lobe about 0.4 times the length of glabella plus occipital ring ; 

 exsagittal distance to posterior margin equal to length of palpebral 

 lobe. Posterior area slender, about as wide (tr.) as occipital ring. 

 Anterior sections of facial suture on the average more divergent than 

 in most species, but there is considerable variability in this character 

 among the population from a single thin bed. Free cheek with well- 

 defined, flat border; genal spine flat dorsally at least in basal part, 

 very long. 



Pygidium twice as wide as long. Outline oval, lacking definite 

 geniculation on anterior margin, widely rounded laterally, not notched 

 but elevated medially. Axis stout, composed of 3 rings plus a terminal 

 section, extended into a broad postaxial ridge that reaches the margin. 

 Pleural platforms downsloping, giving pygidium considerable relief 

 compared to other species. Pleural furrows and grooves shallow, the 

 first furrow curving backward to follow the curvature of the margin. 

 Border flat, poorly defined ; doublure wide laterally, tapering medially. 



Surface of test smooth, except for the genal coeca showing faintly 



