NO. 9 NEW CAMBRIAN TRILOBITE FAUNULE — RASETTI 2$ 



ing to a fairly sharp point, occupying about two-thirds of the 

 cephalic length, unfurrowed. Occipital furrow deeper laterally, 

 impressed throughout ; occipital ring extended into a robust, horizon- 

 tal spine longer than all the rest of the cephalon. Cheeks lowest 

 medially, slightly convex, their outline forming a sharp angle at the 

 posterolateral corner. Border furrow well impressed ; border convex, 

 fairly wide, of about even width but for a slight narrowing toward 

 the genal angle, bearing a few, indistinct tubercles. Posterior border 

 furrow deep and wide ; posterior border with geniculation about half- 

 way between axial furrow and genal angle, the latter lacking a spine. 

 Surface of test smooth. Length of cephalon (exclusive of occipital 

 spine) 3.4 mm, width 3.8 mm. 



Occurrence. — Collection cs-4, North Chatham. 



Discussion. — This form seems referable to Calodiscus even 

 though it differs in several features from all previously described 

 species. Its chief distinguishing characteristics are the relatively 

 short glabella, well-impressed occipital furrow, excessively long occip- 

 ital spine, narrowness of the border furrow, and even width of the 

 border. 



Types.— RoXotypo,: U.S.N.M. 146003. 



LEPTOCHILODISCUS Rasetti, new genus 



Description. — Cephalon of moderate convexity. Glabella defined 

 by deep axial furrow but not rising much above the cheeks, narrow 

 and long, tapered, pointed in front, not reaching the anterior border, 

 unfurrowed. Occipital furrow deep; occipital ring extended into 

 spine. Cheeks everywhere convex, not separated in front by a pre- 

 glabellar depression. Border very narrow, wire-like, well defined by 

 narrow border furrow, narrowest in frontal portion, somewhat wid- 

 ened laterally. Posterior border furrow deep ; posterior border widen- 

 ing distally, with geniculation near genal angle. Surface of test in 

 type species punctate. 



Type species. — Leptochilodiscus punctulatus Rasetti, new species. 



Occurrence. — Late Lower Cambrian of New York. 



Discussion. — This simple eodiscid cephalon does not seem refer- 

 able to described genera. Compared with Calodiscus, it shows impor- 

 tant differences that are sufficient to doubt a close relationship. In 

 Calodiscus the anterior border is much wider, usually widest medially, 

 and the cheeks are separated in front of the glabella by a more or 

 less extended preglabellar depression. The glabella of Leptochilodis- 

 cus is unusually long and pointed. The deep occipital furrow and 

 spinose occipital ring also are not suggestive of Calodiscus. 



