NO. 3 UPPER CAMBRIAN TRILOBITE FAUNAS — RASETTI 49 



tal, somewhat falcate lobes separated by a wide, rounded notch. Mid- 

 length of pygidium 5 mm., width 10 mm. 



Discussion. — The cranidium referred by Resser to Uncaspis tennes- 

 seensis is an example of Modocia duhia, as mentioned in the synonymy 

 of that species. The holotype pygidium is certainly not an Uncaspis, 

 whatever the characters of this poorly understood genus may be, and 

 seems definitely referable to Coosella. This assignment requires a 

 change in the trivial name, because the binomial combination Coosella 

 tennesseensis was used by Resser for another species. The pygidium 

 has fundamentally the same structure as Coosella andreas, but is more 

 strongly bilobate, and the notch between the lobes is much wider. 



Occurrence. — Red beds at the base of the Nolichucky (Cedaria 

 zone) at U.S.N.M. locality 27d, where it was also collected by the 

 author (loc. cnd/1). 



ry/)^.y.— Holotype : U.S.N.M. 94846. Plesiotype: U.S.N.M. 

 144573. 



COOSELLA PLANICAUDA Rasetti, new species 



Plate 7, figures 1-5 



Available material. — A few cranidia and numerous pygidia. 



Description. — Glabella of usual shape, with traces of lateral furrows ; 

 occipital furrow deep and straight, occipital ring bearing a low node. 

 Preglabellar field and border of about equal width (sag.) ; border 

 strongly convex, with terrace lines. Palpebral lobes narrow, half the 

 glabellar length ; width of palpebral area about 0.3 times the glabellar 

 width. Midpoint of palpebral lobes somewhat in advance of glabellar 

 midpoint. 



Pygidium with very little overall relief. Axis moderately convex, 

 little more than half the pygidial length, moderately tapered, showing 

 2 or 3 rings and an unfurrowed terminal section, extended into a brief 

 postaxial ridge. Pleural lobes almost flat, showing faint furrows in the 

 narrow triangular portions anterior to the inner margin of the wide 

 doublure, smooth in the remainder of the broad, slightly concave area ; 

 posterior outline well rounded except for a shallow median notch 

 between the pair of wide lobes. Surface of test smooth. Length of 

 largest pygidium 7.5 mm., width 11 mm. 



Discussion. — This species possibly resembles Coosia more than 

 Coosella in the shape of the pygidium, but the cranidial features rather 

 indicate the present generic assignment. 



Occurrence. — Lower and middle portions of the lower limestone 

 member of the Nolichucky (Crepicephalus zone). Localities cnk/2, 

 cnm/2. 



Ty/)^.y.— Holotype : U.S.N.M. 144574. Paratypes: U.S.N.M. 

 144575-6. 



