FOSSILS GF THE LOWER SILURIAN. 243 



of rib gives to the shield an appearance similar to the groining of a Gothic 

 arch. Margin of the shield surrounded by twelve long, rather strong 

 spines, four of which, on each side, are about equal in size and strength, 

 while the four occupying the posterior border are shorter and unequal, those 

 in the middle being the shortest. 



The peculiar feature of the sj^ecimen consists in the divided ribs of the 

 lateral lobes and spiuose margin. In these features, it differs from all others 

 known, and may possibly, when better material shall be examined, showing 

 other parts of the organism, require a distinct generic name. 



Formation and locaUtij. — In greenish argillaceous slates of the Quebec 

 group, in the canon above Call's Fort, north of Box Elder Canon, Wahsatch 

 Mountains, Utah. Collected by S. F. Emmons, esq. 



Genus BATHYURUS Billings. 

 Batiiyurus Pogonipensis n. sp. 



Plate I, figs. 33-3-1. 



The species is recognized only by the pygidium, which is rather small, 

 measuring a little less than three-fourths of an inch in the greatest trans- 

 verse width, by a length of a little less than half an inch. Form transversely 

 elliptical, the posterior margin nearly twice as convex as the anterior border; 

 lateral extremities angular ; axis -narrow, forming only about one-fourth of 

 the entire width, highly convex, and about three-fourths as long as the 

 entire shield, extremity obtusely rounded and terminating abruptly; marked 

 by four transverse annulations exclusive of the terminal ones, the posterior 

 one being as long as the two next preceding it ; rings highly convex and 

 rounded, with interspaces of nearly equal dimensions. Lateral lobes broad 

 and somewhat triangular; the inner third of the width horizontal, beyond 

 which the surface slopes rapidly to the outer margin ; marked by thi-ee 

 broad, slightly flattened, but strong and very distinct ribs, which terminate 

 about one-third of the width within the marg-in,- leaving a plain border sur- 

 I'ounding the shield. The two anterior ribs are broad, and show a faint 

 depression along the middle in the upper part. Surface of the cnist, under 

 an ordinary magnifying power, apparently smooth, except on the crest of 

 the axial rings, where thei'e are a few node-like granules 



