NO. 9 NEW CAMBRIAN TRILOBITE FAUNULE — RASETTI 33 



Ion, extended downward into a series of short spines somewhat 

 visible in dorsal view by producing a wavy outline; seven or eight 

 pairs of such spines are usually present. A. R, Palmer (private com- 

 munication) suggested to the writer that such spines may fit the 

 reverse side of the tubercles of the cephalic border when the animal 

 is enrolled. The structures in the present species may support this 

 interpretation since the tubercles and spines are in about equal num- 

 bers and similarly spaced. 



Surface of cephalon and pygidium densely covered with fine gran- 

 ules. Length of largest cephalon 11 mm, width 11 mm. The entire 

 pygidia recovered are somewhat smaller. 



Occurrence. — Collection cs-4, North Chatham. 



Discussion. — Even though the close affinity to typical species of 

 Serrodiscus can hardly be doubted, this form presents numerous 

 differences from all those previously described. The most conspicu- 

 ous features are the great convexity of the cephalon, depth of the 

 axial furrows, unusual length and somewhat clavate shape of the 

 glabella, and un furrowed pygidial axis bearing a spine. The most 

 similar form is an undescribed species from the Purley Shales of 

 England (Rushton, private communication). 



Types.— Uo\oty^e: U.S.N.M. 146022. Paratypes: U.S.N.M. 

 146023. 



SERRODISCUS SPINULOSUS Rasetti, new species 



Plate 7, figures 7-11 



Available material. — A few cephala and one pygidium. 



Description. — Glabella with undifferentiated occipital ring widest 

 at posterior end, narrowed forward for a short distance, then parallel- 

 sided, strongly tapered in frontal portion and rather pointed medi- 

 ally, un furrowed. Glabella of moderate convexity, anteriorly reaching 

 the border on account of a sharp median inbend of the border furrow 

 which thus merges for a short distance with the axial furrow. Occipi- 

 tal ring bearing a short spine. Cheeks slightly convex, downsloping. 

 Border widest medially on account of the above-mentioned feature 

 of the border furrow, narrowing toward the genal angle, bearing 

 several pairs of very low, somewhat indistinct tubercles. Posterior 

 border wide (exsag.), extended into short, sharply pointed genal 

 spine. No geniculation features on posterior cephalic margin between 

 axial furrow and genal spine. Cephalic border narrowest at postero- 

 lateral angles in front of genal spine. 



Pygidium referred to the species with long, totally unfurrowed 

 axis almost reaching posterior border. Articulating half-ring expanded 



