[MATTHEW] STUDIES ON CAMBRIAN FAUNAS 189 



Messrs. Hall and Whittield, but the main pleural furrow does not run 

 down on the spine, there being a flattened margin all around that limits 

 it. Our example is larger than the type, and shows only live laleral 

 spines, but there may be six on a perfect shield. 



Sculpture. — Under a strong lens the surface is seen to be very tinely 

 granulose, especially on the spines. 



Size. — Length of pygidium, 15 or 20 mm.; width exclusive of the 

 spines, 30 mm. 



Horizon. — Limestone bands of the gi-ay shales. 



DoRYPYGE QUADRICEPS, Hall k Whitfield, sp. (PI. lY., figs. 2a and b.) 



Dikellovephalus quadricejis, H. & W. Geol. Expl., 40th par., vol, iv., p. 240, pi. i., 

 flgs. 37 to 40. 



Dikellocephalus quadriceps. Wale, U. S. Geol. Surv., vol. viii., p. 45, pi. ix., llg;. 

 24. 



Olenoides quadriceps, Wale, U. S. Geol. Surv. Bull., '.iO, p. 187, pi. xxix., figs. 1, 

 la to c. 



var. VALIDA n. var. (PI. IV., figs. 2c and d.) 



Among the pygidia of the tauna under consideration is one which 

 does not seem to be specifically distinct from the species above quoted. 

 Apparently it ditfers only in having a wider and more prominent rachis. 



The description of Hall and Whitfield's type is as follows : "A 

 pygidium associated with the glabella is paroboloid in form and sur 

 rounded on the margins by twelve short, rather strong spines, the four 

 on the posterior margin being shorter than the others. Axis narrow, 

 highly convex, two-thirds as long as the shield, and marked by four 

 rings exclusive of the terminal one ; lateral lobes, broad, and marked by 

 four low rounded ribs, the anterior one much narrower than the others ; 

 each of the four ribs terminating in one of the lateral spines.' 



The St. John variety ditt'ers in having a broader rachis, which is 

 more markedly elevated at the extremity than that of Hall and Whit- 

 field ; the ribs also are more prominent at the ends and ai'e marked by a 

 faint pleural groove the terminal lobe of the rachis is shorter, and the 

 flattened border more abruptly divided from the costae. 



Sculpture. — The surface is covered with minute granulations, visible 

 with a lens. 



Size. — Length of the pygidium exclusive of the spines. 4 mm.; 

 width at the front, 8 mm. 



Horizon. — Found with the preceding, also in phosphate nodules in 

 a conglomerate band. 



Sec. IV., 1897. 11. 



