88 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 148 



Species, half as wide as glabella. Ocular ridges transverse or even 

 slightly slanted forward. Palpebral lobe averaging 0.4 times the gla- 

 bellar length. Distance from posterior end of palpebral lobe to posterior 

 margin equal to length of palpebral lobe. Anterior section of facial 

 suture of average divergence. Posterior area as wide (tr.) as occipital 

 ring. 



Free cheek with slightly convex border like the cranidium; genal 

 spine flat, of average length. 



Pygidium somewhat less than 3 times as wide as long, transversely 

 subelliptical. Axis relatively long, showing 2 or 3 rings plus a ter- 

 minal section, well defined on outer surface. Pleural lobes with well- 

 impressed furrows and very shallow interpleural grooves visible on 

 outer surface. Posterior margin slightly indented medially. 



Length of largest cranidium collected 8 mm. Length of largest pygi- 

 dium 3.6 mm., width 10 mm. 



Discussion. — The cranidium of this species is almost indistinguish- 

 able from A. huttsi except for the shallower glabellar and axial fur- 

 rows. Even this difference can be determined statistically only when 

 numerous well-preserved specimens in limestone are available. The 

 pygidium, however, is markedly distinct in possessing one less seg- 

 ment both in the axis and pleural lobes, and in its posterior outline 

 which is slightly notched medially, like A. walcotti and several other 

 species, rather than somewhat pointed as in ^. huttsi. The interpleural 

 grooves are less distinct than in that species. 



Occurrence. — The type locality is cnp/14. Shields Ridge. Also 

 collected at localities cnp/15. Three Springs, and cnp/20, Washburn. 

 A few, small cranidia apparently identical with topotypes of the same 

 size were recovered from considerably higher beds at locality cnr/4, 

 Lost Creek. Since several species of Aphelaspis are distinguishable 

 only from the pygidia, the identification must be considered tentative. 



Types.— Ro\oty^&: U.S.N.M. 144659. Paratypes: U.S.N.M. 

 144660-2, 144734. 



APHELASPIS TRANSVERSA Rasetti, new species 



Plate 16, figures 21-27 



Description. — Cranidium wide and short, of the same general 

 proportions as in A. lata. Glabella of considerable transverse con- 

 vexity, defined by a rather deep axial furrow at the sides, a shallower 

 furrow in front, truncate. Occipital furrow deeper than usual in the 

 genus; occipital ring bearing a small node. Preglabellar field with 

 considerable convexity on midline ; border furrow straight at the sides, 

 forming a rounded, obtuse angle medially. Border sharply upturned 

 from preglabellar field, almost flat; sagittal border length two-thirds 



