108 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 148 



plus a terminal section, almost reaching posterior margin. Pleural re- 

 gions of low convexity, with almost equally deep pleural furrows and 

 interpleural grooves, curving back distally and almost reaching the 

 margin. Border furrow and border almost indistinct. Length of a large 

 pygidium 6.5 mm., width 13 mm. 



Discussion. — This form differs from the type species in many details 

 of the cranidium, such as the lesser prominence of the glabella, lesser 

 divergence of the anterior sections of the facial suture, and more 

 anterior position of the eyes. 



Occurrence. — The type locality is U.S.N.M. 27d; red beds at the 

 base of the Nolichucky {Cedaria zone) near Roger sville. Collected by 

 the author at the same locality (cnd/1) and also in the uppermost beds 

 of the underlying Maryville limestone (localities cnc/1 to cnc/6) . 



Types. — Holotype and paratypes: U.S.N.M. 94845. Paratype of 

 Asaphiscus ? agatho: U.S.N.M. 62820. Paratype of Uncaspis tennes- 

 seensis: U.S.N.M. 94846. Plesiotypes figured herein: U.S.N.M. 

 144715-6. 



MODOCIA BIDENTATA Rasetti, new species 



Plate 1, figures 13-21 



Available material. — Numerous cranidia and pygidia in limestone. 



Description. — Glabella rather convex, rising above the cheeks, rela- 

 tively narrow and long, unfurrowed. Occipital furrow well marked; 

 occipital ring short, simple. Frontal and palpebral areas downsloping ; 

 preglabellar field longer (sag.) than border width ; border well defined, 

 slightly convex, tapered in width at the sides. Palpebral area about 

 half the glabellar width; ocular ridges faint; palpebral lobes located 

 somewhat in advance of glabellar midpoint. Anterior sections of facial 

 suture somewhat divergent ; posterior section curving backward, pro- 

 ducing blunt posterior area. 



Pygidium of same general proportions as in preceding species, not 

 greatly convex transversely. Axis as in preceding species. Pleural 

 regions with pleural furrows and interpleural grooves of progressively 

 decreasing strength. First pleural segment extended into a pair of 

 short, backward-directed marginal spines. 



Surface of test smooth. Length of largest cranidium 17 mm. Length 

 of largest pygidium 8.5 mm., width 17 mm. 



Discussion. — The cranidial proportions are fully typical of Modocia. 

 The chief distinguishing feature is the pair of short pygidial spines. 

 This character is not uncommon in several genera of late Medial Cam- 

 brian and Dresbachian ptychoparioid trilobites, e.g., in species of 

 Ehmaniella. 



