MARYLANP GEOLOGICAL SURVEY 323 



ORTHOCEKAS ARCUOLIRATUM Hall 

 Plate XLVIII, Fig. 22 



Orthoceras arcuoliratum Hall, 1847, Pal. New York, vol. i, p. 198, pi. xlii, 

 figs. 7a-c. 



Description. " Slender, very gradually tapering to an acute point ; 

 surface marked by strong and extremely arching or undulating annula- 

 tions, and obscurely, by fine longitudinal striae; annulations about 

 equalling the spaces between them ; outer chamber and aperture unknown ; 

 section circular; siphuncle central. 



" The distinguishing features of this species are its slender form and 

 extremely arched annulations, which, in half the circumference, ascend 

 twice the width of the space between each annulation. All the other 

 annulated species have the ridges less arched upon the back." Hall, 1847. 



Occurrence. CHAMBERSBURG LIMESTONE (Greencastle bed). Green- 

 castle, Pennsylvania. Trenton limestone of New York. 



Collection. TJ. S. National Museum. 



ORTHOCERAS JUNCEUM Hall 

 Plate LI, Figs. 4-7 



Orthoceras juncevm Hall, 1847, Pal. New York, vol. i, p. 204, pi. xlvii, 



figs. 3a-f. 

 Orthoceras junceum Clarke, 1897, Minnesota Geol. and Nat. Hist. Surv., Pal., 



vol. iii, pt. 2, p. 790. 



Description. " Slender, tereta-cylindrical, tapering very gradually ; 

 septa thin, distant from one-fourth to one-third the diameter; outer 

 chamber deep; siphuncle small, central; section circular; surface finely 

 striated transversely, but without longitudinal striae." Hall, 1847. 



This rather frequently quoted species has received no further study 

 since Hall's original description in 1847 and it is probable that many 

 misidentifications of it have been made. However, fragments of an 

 Orthoceras from the basal Martinsburg shale of southern Pennsylvania 

 agree so well with typical specimens of 0. junceum from the type locality 

 that it is believed the present identification is correct. 



Occurrence. MARTINSBURG SHALE (Sinuites bed). Chambersburg, 

 Pennsylvania. Trenton limestone of New York. 



Collection. U. S. National Museum. 



