NO. 3 CAMBRIAN AND OZARKIAN TRILOBITES 75 



The species now referred to the genus from the Mons formation, 

 in the present stage of the study, are : 



Briscoia glaiicus W dilcoit. 

 B. onophas Walcott. 

 B. opimius Walcott. 

 B. sinclairensis Walcott. 

 B. splendens Walcott. 

 B. zebina Walcott. 



There should also be included : 



B. limbatus (Hall) =i Dlkelocephalus ? Umbatus Hall (Walcott).* 

 B. coloradoensis Walcott =^Saukia coloradoensis Walcott." 



BRISCOIA SINCLAIRENSIS Walcott 



Plate 20, figs, i-io 



Briscoia sinclairensis Walcott, 1924, Smithsonian Misc. Coll., Vol. 75, No. i, 

 P- 27, fiff- 9- 



Description. — This is the largest species of the genus although 

 B. splendens is close to it in size. The material representing the cepha- 

 lon is far from satisfactory, but by combining data from several 

 specimens a fairly satisfactory outline is obtained. Glabella with 

 nearly parallel straight sides and broadly rounded front ; rather 

 strongly convex and marked by a distinct narrow occipital furrow 

 that bends slightly forward towards the ends ; the first furrow is 

 narrow and distinct ; it slopes forward from near the center and 

 terminates just within the lateral margin, not entering the dorsal 

 furrow ; the second furrow is represented by a short furrow on each 

 side corresponding to the lateral third of the second furrow ; the 

 anterior lobe of the glabella is smooth, sloping rather abruptly down 

 to the faint dorsal furrow between it and the frontal limb; the first 

 and second lobes are rather slightly convex and a little wider than 

 the occipital lobe which is flattened and without a node at its central 

 posterior margin. Dorsal furrow beside the glabella narrow and 

 distinct ; both the glabella and fixed cheeks rise abruptly from it. 



Fixed cheeks narrow, expanding in front to merge into the frontal 

 limb and posteriorly widening a little as they join the narrow posterior 

 limbs ; palpebral lobes nearly one-third the length of the cranidium, 

 narrow and with a well-defined furrow within the outer margin ; 

 frontal limb broad, about one-fifth the length of the cranidium; it 

 is nearly flat but rises slightly towards the slightly convex frontal rim 



* Smithsonian Misc. Coll., 1914, Vol. 57, No. 13, pi. 65, figs. 5-8. 

 ^ Loc. cit, p. 27^, text figs. 14-16. 



