314 Systematic Paleontology — Middle Devonian 



Description. — " The tube is slender and the enlargement very gradual. 

 Air-chambers, septa and siphuncle unknown. Surface marked by reg- 

 ular, numerous, low, rounded transverse ridges, about twelve in the 

 space of ten mm. ; the interspaces, or furrows, are regularly concave, and 

 have a width equal to the ridges; portions of the surface also show that 

 it was traversed by fine, sharp, longitudinal striae, crossing the ridges." 

 Hall, 1879. 



The Maryland specimen is apparently a fragment of the living cham- 

 ber 80 mm. in length which is marked by transverse ridges and furrows 

 with 10 to 12 ridges in the space of 10 mm., and in appearance very 

 similar to those represented on the figure of this species in the Palaeon- 

 tology of New York.' 



Occurrence. — Eomney Formation, Hamilton Member. Road east 

 of Pine Hill about 4 miles north of Oldtovm. 



Collection. — Maryland Geological Survey. 



Family KIONOCERATIDAE 



Genus SPYROCERAS Hyatt 



Spyroceras crotalum (Hall) 

 Plate XLI, Figs. 1-5 



Orthoceras crotalum Hall, 1861, Descriptions of New Species of Fossils, etc., 



p. 50. 

 Orthoceras crotalum Hall, 1S62, Fifteenth Rep. N. Y. State Cab. Nat. Hist., 



p. 78. 

 Orthoceras crotalum Hall, 1879, Pal. N. Y., vol. v, pt. ii, p. 296, pi. xlii, figs. 



1-9, 11, 12; pi. Ixxxii, figs. l-G; pi. cxiii, fig. 13. 

 Spyroceras crotalum Keyes, 1891, Johns Hopkins Univ. Circ, vol. xi, p. 29. 

 Orthoceras (Spyroceras) crotalum Clarke, 1903, N. Y. State Mus., Bull. 65, 



p. 622. 

 Spyroceras crotalum Grabau and Shimer, 1910, N. Am. Index Fossils, vol. ii, 



p. 64. 



Description. — Shell straight, regularly and rapidly enlarging from the 

 apex, and becoming cylindrical toward the aperture; transverse section 

 subcircular. Living-chamber small, cylindrical; length about two and a 



* Vol. v, pt. ii, pi. 84, fig. 18. 



