34 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I48 



medially as in preceding species. Pleural lobes of moderate con- 

 vexity; border furrow well impressed. Border fairly wide, convex, 

 extended ventrally into a series of short spines, producing in dorsal 

 view a waviness of the margin. Seemingly there was a spine on the 

 posterior part of the axis. 



Surface of test of cephalon and pygidium perfectly smooth. Length 

 of largest cephalon 5.6 mm, width 5.2 mm. Length of pygidium 

 4.7 mm, width 5.6 mm. 



Occurrence. — Collection cs-4, North Chatham. 



Discussion. — This form is fully typical of Serrodiscus in all respects 

 excepting one unusual feature, the inbend of the anterior border 

 furrow causing it to merge with the axial furrow. Other distinguish- 

 ing features are the occipital and genal spines, the shape of the 

 glabella, and the unfurrowed pygidial axis. 



Ty/>^.j.— Holotype: U.S.N.M. 146026. Paratypes: U.S.N.M. 

 146027. 



SERRODISCUS LATUS Rasetti, new species 

 Plate 10, figures 12-15 



Available material. — Three cephala, of which one excellently pre- 

 served. 



Description. — Glabella with totally undifferentiated occipital ring 

 slightly tapered, straight-sided, well defined by deep axial furrows, 

 somewhat pointed in front, almost reaching the border, unfurrowed. 

 Cheeks convex, rising somewhat above the axial furrows, steeply 

 sloping to border furrow at the sides. Border furrow deep all around 

 the cheeks, medially almost meeting the axial furrow. Border some- 

 what convex and on the average horizontal, widest medially and but 

 slightly tapering to the genal angle, bearing a few pairs of low 

 tubercles. Posterior border furrow and border about as wide as 

 lateral border ; posterior cephalic margin straight and transverse from 

 axial furrow to geniculation, then turning downward and forward to 

 the genal angle which bears a minute spine. Surface of test smooth. 

 Length of largest cephalon 5.0 mm, width 6.2 mm. 



Occurrence. — Collection cs-4, North Chatham. 



Discussion. — The cephalic features agree with Serrodiscus, but in 

 the absence of a pygidium it is questionable whether the species 

 should not rather be referred to Calodiscus, or possibly Cohholdites. 

 The cephalon differs markedly from C. speciosus and other described 

 species in the general outline, regularly curved in front rather than 

 pointed, deep axial furrows, and great convexity of the cheeks. 



