NO. 13 DIKELOCEPHALUS AND OTHER GENERA 385 



Formation and locality. — Upper Cambrian: (346f) Beneath the 

 Natural Bridge limestone ; soft, shaly-yellow rock, probably a decom- 

 posed thin-bedded dolomitic limestone, east side of road about 1.5 

 miles (2.4 km.) north-northeast of Natural Bridge, south end of 

 Rockbridge County, Virginia (Dr. Freeman Ward of Yale Uni- 

 versity, 191 1 ). 



Genus OSCEOLIA, new genus 



This genus is known only by the cranidium, associated free cheeks 

 and pygidium of the type species. These parts occur together in the 

 same layer of sandstone to such an extent that it seems reasonable to 

 consider them as belonging to the species Osceolia osceola (pi. 68, 

 figs. 4-10) . The strong concave frontal limb, broadly conical glabella, 

 and long palpebral lobe serve to distinguish the cranidium from that 

 of Dikclocephalus (pis. 60-63), Sankia (pis. 65, 66) 2iX\<l .Calvinella 

 (pi. 70). 



The pygidium is characterized by the very strong extension of the 

 anterior segment (pi. 68, figs. 8-10), and in being shorter and more 

 transverse than the pygidium of the three genera mentioned above. 



All of the specimens of the typical species 0. osceola occur in a 

 rather friable sandstone so that little is known of the surface char- 

 acters. As far as known the genus may be briefly characterized as 

 follows : 



Cephalon transversely semicircular with a broad convex frontal 

 limb; genal angles extended into postero-lateral spines. 



Glabella obtusely conical, with sides converging slightly to the 

 rounded front. Occipital segment rounded and defined by a narrow, 

 strong furrow from base of glabella. Posterior glabellar furrow 

 strong and extending across the glabella. 



Fixed cheeks very narrow ; palpebral lobes elongate and extending 

 back of the line of the occipital furrow. Facial suture back of the 

 palpebral lobes extending almost directly outward well towards the 

 genal spine so as to outline a very narrow postero-lateral limb ; curv- 

 ing around the palpebral lobes they extend forward with a slight out- 

 ward curve nearly across the frontal limb and then curve gently 

 inward to the front margin. Free cheeks large. 



Associated pygidium nearly twice as broad as long with strong 

 median axis. 



Genotype.- — Dikclocephalus osceola Hall (1863). 



Osceolia is represented by a single species that is readily distin- 

 guished by its strong, concave frontal limb, large palpebral lobes, 

 narrow fixed cheeks and transverse pygidium with the great spinous 

 extension of the pleurse of the first segment. 



