NO. 9 NEW CAMBRIAN TRILOBITE FAUNULE — RASETTI 39 



tion. Ring furrows with peculiar structure, deepening to pair of pits 

 at the sides some distance from the axial furrow ; the medial portion 

 of the ring furrow narrower and shallower, concave toward the front. 

 The axial rings bore spines of decreasing length, broken off in the 

 available specimens. Pleural regions un furrowed, downsloping ; bor- 

 der furrow narrow but deep ; border narrow, but expanded into four 

 pairs of wide, short, somewhat blunt spines about evenly spaced. 

 The spines are directed outward, not downward as in many species 

 of Serrodiscus. Surface of test smooth. Length of largest pygidium 

 5.7 mm. 



Occurrence. — Collection cs-4. North Chatham. 



Discussion. — It is questionable whether this peculiar pygidium 

 belongs to any of the cephala known from the locality. 



Disposition of material. — Figured specimens: U.S.N.M. 146034. 



Undetermined pygidium No. 3 

 Plate 10, figure 11 



Available material. — A single, well-preserved example. 



Description. — Pygidium of low convexity, almost semicircular. 

 Axis defined anteriorly by very shallow axial furrows, the remainder 

 undifferentiated from the pleural regions. Articulating half -ring and 

 furrow well defined. Anterior outline straight in dorsal view, with 

 geniculation about halfway between axial furrow and anterior angle, 

 with border bent downward but not appreciably backward. Border 

 furrow well impressed, border flat, of almost even width throughout. 

 Doublure vertical, narrow, with smooth margin. Surface of test 

 smooth. Length of pygidium 7.0 mm, width 10.3 mm. 



Occurrence. — Collection cs-4. North Chatham. 



Discussion. — In the general shape this pygidium recalls Litomefo- 

 pus longispinus, but differs markedly in the lesser convexity and 

 especially in the almost complete obsolescence of the axial furrows. 

 It should presumably be associated with a cephalon with poorly 

 differentiated glabella, but no such form is present in the collection. 



Disposition of material. — Figured specimen: U.S.N.M. 146035. 



Family OLENELLIDAE Vogdes, 1893 



Olenellids are relatively common in the faunule, but owing to the 

 thinness of their test, they are usually much more fragmentary than 

 the Eodiscids. Cephala of three different species have been identified. 



