NO. 3 UPPER CAMBRIAN TRILOBITE FAUNAS — RASETTI 95 



narrower (tr.) than occipital ring. Free cheek with flat border well 

 defined by lateral border furrow, which, however, becomes indistinct 

 before meeting posterior border furrow, as in all species of Aphelaspis. 

 Genal spine flat, of average length. Facial suture cutting posterior 

 margin somewhat farther from genal angle than in A. arses. 



Surface distinctly pitted in furrows on cranidium and free cheeks, 

 especially in border furrow. Length of unusually large cranidium 

 exclusive of spine, 13 mm. ; the majority do not exceed 8 mm. 



Pygidium transversely ovate, two and one-half times as wide as 

 long. Axis stout, showing 2 rings and a terminal section, almost reach- 

 ing the margin. Pleural lobes almost flat and horizontal. Anterior and 

 posterior outlines slightly and regularly curved, lateral angles well 

 rounded. Anterior pleural furrow distinct, distally curving backward 

 to parallel the margin ; another pair of furrows indistinct. The surface 

 in the depressions in some specimens is pitted as in the cranidium and 

 free cheeks. Length of largest pygidium 3.5 mm., width 8.5 mm. 



Discussion. — This species can be distinguished from the closely 

 related A. arses by the shallower axial furrow, almost horizontal pal- 

 pebral area, indistinct palpebral furrow, the characteristic pitted sur- 

 face in the depressions of the test, and somewhat different shape and 

 flat border of the free cheek. 



Occurrence. — This species occupies a somewhat higher stratigraphic 

 position than A. arses and is frequently associated with A. tumifrons. 

 The type locality is cns/2. Also present in collections cns/1, cnt/1, 

 cnt/4, cns/15, cnt/15, cntV15, cnt/20, cntV20, cnt/21, and Oder's 

 collection No. 14. 



Types.— Uolotype: U.S.N.M. 144677. Paratypes: U.S.N.M. 

 144678-80. 



Genus APHELASPIDELLA Rasetti, new genus 



Description. — Cranidium similar to Aphelaspis, except in the very 

 strong divergence of the anterior sections of the facial suture. Free 

 cheek as in Aphelaspis, with long genal spine. Pygidium proportion- 

 ately much larger than in Aphelaspis. Axis occupying less than half 

 the length, extended into a postaxial ridge. Pleural lobes wide, with 

 little relief, with shallow furrows and grooves and a wide, concave 

 border ; doublure very wide. 



Discussion. — The very close relationship to Aphelaspis is obvious. 

 However, the different course of the anterior section of the facial 

 suture and the pygidial characters are important enough to deserve 

 generic recognition. 



Type species. — Aphelaspidella macropyge Rasetti, n. sp. 



Occurrence. — Aphelaspis zone of the southern Appalachians. 



