Maryland Geological Survey 415 



to be suggestive of this and also of its similarity to S. trihulis, with which 

 it should not be confounded since it has fewer and more widely separated 

 plications and is also less transverse. 



After describing this species the writer saw Weller's account of his 

 Metaplasia plicata ' which seems to be very closely related. The only dif- 

 ferences are that the New Jersey form attains larger growth and the plica- 

 tions are more depressed and broader. Larger collections may show that 

 S. trihuwi-ius and M. plicata are but local expressions of the same species. 



Occurrence. — Ohiskany Formation, Shriver Member. Cash Valley, 

 Nicholas Mountain, and Winchester Eoad near Cumberland. 



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



Spirifer arenosus (Conrad) 

 Plate LXXI, Figs. 1-9 ; Plate LXXII, Fig. 1 



Delthyris arenosa Conrad, 1839, Third Ann. Rept. N. Y. Geol. Surv., p. 65. 

 Spirifer arenosus Hall, 1859, Nat. Hist. N. Y., Pal., vol. iii, p. 425, pi. xcviii, 



figs. 1-8; pi. xcix, figs. 1-10; pi. c, figs. 1-8. 

 Spirifera arenosa Hall, 1883, Second Ann. Rept. N. Y. State Geol., pi. Iv, figs. 



3-7. 

 Spirifer arenosus Hall and Clarke, 1893, Nat. Hist. N. Y., Pal., vol. viii, pt. ii, 



pp. 24, 27, 37, pi. xxix, figs. 1-4; pi. xxx, figs. 3-8. 

 Spirifer arenosus Clarke, 1900, Mem. N. Y. State Mus., vol. iii. No. 3, p. 46. 



Description. — " Shell trigonal, with radiating sulci; superior valve with 

 a rounded elevation in the middle, having about 4 sulci upon it, or 5 ribs; 

 inferior valve, with a corresponding furrow ; basal margin undulated, 

 prominent and angulated in the middle. Length 2^ inches. Locality: 

 Helderberg, in sandstone." Conrad, 1839. 



" Shell, in the young state, semielliptical, with the beak a little elevated 

 above the hinge-line; the old shell becoming ventricose, and the beak 

 much elevated above the hinge-line, having a somewhat semioval form. 

 The proportions vary from length and width equal, to width one-third 

 greater than the length. Cardinal angles sometimes produced in acute 

 terminations, but usually rounded, particularly in old shells. 



" Ventral valve very regularly convex, the greatest convexity about 

 one-third the distance below the beak. The cardinal angles, when pro- 



' Geol. Surv. N. J., Pal., vol. iii, 1903, p. 356, pi. xlviii, figs. 7-12. 



