MARYLAND GEOLOGICAL SURVEY 345 



the pygidium from the posterior margin; plurae convex, smooth in the 

 larger individuals, but in younger ones marked by about ten obscure 

 segments, which also continue across the axis; the entire margin of the 

 pygidium, except where it joins the thorax, bordered by a rather broad, 

 slightly depressed, marginal border; the anterior, lateral angles bent 

 abruptly downward." Weller, 1903. 



This frequently quoted trilobite has been often described and illustrated 

 with the result that several species have undoubtedly been confused under 

 the name. The specimens from the Cumberland Valley are fragmentary, 

 although they agree so far as they go with the above description. The 

 complete examples figured are from the type area of the species in New 

 York. 



Occurrence. CHAMBERSBURG LIMESTONE (Christiania bed). Penn- 

 sylvania, Maryland, and Virginia. 



Collections. Maryland Geological Survey, U. S. National Museum. 



. ISOTELUS Sp. 



Plate XXXVII, Fig. 9 



Description. A single imperfect free cheek of Isolelus has been found 

 in the Frederick limestone and is figured in the present report. It is of 

 little value in determining the age of this limestone, as species of this 

 general type have a long geologic range. 



Occurrence. FREDERICK LIMESTONE. Just east of Frederick, Mary- 

 land. 



Collection. U. S. National Museum. 



Genus ASAPHELLUS Callaway 



ASAPHELLUS GYRACANTHUS Eaymond 



Plate XXXII, Figs. 8-10 



Asaphus canalis? Cleland, 1900 (not Conrad), Bull. Amer. Pal., vol. ill, 



p. 128, pi. xvi, figs. 7, 8. 



Isotelus canalis Weller, 1902, Pal. New Jersey, vol. iii, p. 132, pi. v, figs. 5, 6. 

 Asaphellus gyracantJius Raymond, 1910, Ann. Carnegie Mus., vol. vii, No. 1. 



p. 39, pi. xiv, figs. 5-7. 



