MARYLAND GEOLOGICAL SURVEY 325 



This seems to be a well-defined species since the specimens from 

 southern Pennsylvania show no apparent deviation from Hall's figures. 

 Unfortunately these specimens are no better preserved than the types 

 and it is impossible to add anything to the above description except to 

 record the occurrence in new localities. 



Occurrence. MARTINSBURG SHALE (Fairview division). Tuscarora 

 Mountain, one and one-half miles east of McConnellsburg, Pennsylvania. 

 Pulaski shale of New York. 



Collection. U. S. National Museum. 



Family CYCLOCERATIDAE 



Genus SPYROGERAS Hyatt 



SPYROCERAS B'ILINEATUM (Hall) 



Plate LI, Figs. 1-3 



Orthoceras Ulineatum Hall, 1847, Pal. New York, vol. i, p. 35, pi. vii, 



figs. 4, 4a. 

 Orthoceras bilineatum Clarke, 1897, Geol. Minnesota, vol. iii, pt. 2, p. 786, 



pi. xlvii, figs. 20, 21; pi. liv, figs. 6, 7. 



Description. Shell comparatively small, gradually expanding, sub- 

 circular in cross-section. Surface smooth over the apical region; con- 

 centric annulations then develop, very obscure at first, but increasing in 

 strength, until they become strong, oblique, or undulating ridges which 

 are broad and most conspicuous near the aperture. Like these annula- 

 tions the interspaces, which are somewhat wider, also become broader 

 toward the body-chamber. An average complete shell probably has a 

 length of about 150 mm. with an apertural diameter of not more than 

 20 mm. 



Surface ornamented by coarse and fine vertical, elevated lines, crossed 

 by extremely fine horizontal lines. Slight nodes or projections mark- the 

 crossing of the two sets of lines. The smooth portion of the shell near 

 the apex exhibits the vertical lines in two simple series. With growth 

 the lines increase in number and the alternation in size of the striae 

 becomes less pronounced. The horizontal striae are quite delicate and 

 often not visible at all. 



