28 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I48 



manner that the anterior portion was bent under the posterior part, 

 but nevertheless recognizable, has a width of 30 mm excluding the 

 genal spines. 



Pygidium 1.4 times wider than long. Axis well defined by the 

 axial furrow, just touching the border furrow, not showing segmen- 

 tation except for the articulating half -ring. Pleural regions convex. 

 Anterior border with sharp geniculation at two-fifths the distance 

 from axial furrow to lateral angle ; facet well developed. Lateral bor- 

 der flat, defined by sharp change in slope, widening from anterior 

 angle to midlength, then narrowing again, narrowest medially. Dou- 

 blure somewhat wider than border, marked with terrace lines that fol- 

 low the blunt serrations of the margin. Surface pitted like the cepha- 

 lon. Length of largest pygidium 16 mm, width 22 mm. 



From the proportions of the various parts and the size of the 

 largest cephalon, the presence of individuals about 50 mm long may 

 be inferred. This may be the largest size for an Eodiscid ever 

 reported. 



Occurrence. — Collection cs-4. North Chatham. 



Types.— Uoloty^: U.S.N.M. 146012. Paratypes; U.S.N.M. 

 146013. 



OODISCUS Rasetti, new genus 



Description. — Cephalon tending to a subquadrate shape. Gla- 

 bella with undifferentiated occipital ring ovate, occupying more than 

 one-third of the cephalic width, strongly elevated, totally unfurrowed. 

 Preglabellar field short (sag.) . Cheeks convex and downsloping. Bor- 

 der furrow and border well defined all around the cephalon; lateral 

 border may show one or two pairs of short spines ; in one species 

 the frontal border bears a pair of tubercles. Posterior border with 

 sharp geniculation and short spine at one-third the distance from axial 

 furrow to rounded genal angle. 



Pygidium with tapered, unfurrowed axis not reaching posterior 

 border. Border furrow and border as in cephalon; border lacking 

 marginal spines. 



Type species. — Oodiscus subgranulatus Rasetti, new species. 



Occurrence. — Late Lower Cambrian of New York. 



Discussion. — The type species and others included in the genus 

 have a rather simple structure which, nevertheless, distinguishes them 

 clearly from previously known Eodiscidae such as Serrodiscus and 

 Calodiscus. The glabella is wider relative to the entire cephalon than 

 in these genera, and has an oval shape ; the undifferentiated occipital 

 ring extends farther back than usual relative to the cheeks. The 



