238 SYSTEMATIC PALEONTOLOGY 



" The interior of the ventral valve shows a narrow area, broad delthy- 

 rium, spondylium almost free from the bottom of the valve, and a median 

 septum that may have supported the front end of the spondylium. In 

 young and strongly convex shells the spondylium is narrow and very 

 strongly defined. The narrow area of the dorsal valve is divided by a 

 broad delthyrium, in the center of which is a very slightly developed 

 cardinal process." Walcott, 1912. 



Occurrence. CONOCOCHEAGUE LIMESTONE. Near Scotland, Franklin 

 County, Pennsylvania, and the same horizon near Funkstown, Maryland, 

 furnish fragments apparently of this species. Upper Canadian and 

 lowest Ordovician of Utah, New Mexico and Colorado. 



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



Family ORTHIDAE 



Genus HEBERTELLA Hall and Clarke 



HEBERTELLA BOREALIS (Billings) 



Plate XXXVIII, Figs. 9-12; Plate XLI, Fig. 17 



OrtMs borealis Billings, 1859, Canadian Nat. Geol., vol. iv, p. 436, fig. 14. 

 Orthis borealis Billings, 1863, Geol. Canada, p. 129, fig. 56, p. 167, fig. 148. 

 Heltertella borealis Raymond, 1911, Ann. Carnegie Mus., vol. vii, No. 2, 

 p. 241, text figs. 13, 14. 



Description. " Shell transversely oval, width at hinge considerably 

 less than the width below. Sides rounded, front straight or slightly 

 rounded. There is a low, broad depression in both valves. The pedicle 

 valve is the more convex of the two in young specimens, but in mature 

 shells the brachial valve is slightly the larger. The cardinal area of the 

 pedicle valve is high and incurved, with a narrow delthyrium. The sur- 

 face is marked by from 20 to 30 broad, simple plications, separated by 

 very narrow grooves." Raymond, 1911. 



Occurrence. STONES EIVER LIMESTONE (Middle division). Near 

 Maugansville, Maryland; Chambersburg, Pennsylvania. 



CHAMBERSBURG LIMESTONE (Caryocystites bed). Fort Loudon and 

 Blue Spring, Pennsylvania. 



A not uncommon Chazyan fossil in Canada and New York. In east 

 Tennessee the species occurs in the Lenoir (Middle Chazyan) limestone. 



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



