Maryland Geological Survey 411 



Spirifer murchisoni Castelnaii 

 PlateLXX, Figs. 1-5 



Spirifer murchisoni Castelnau, 1843, Essai Syst. Sil. I'Amer. Septent., p. 41, 



pi. xii, figs. 1, 2 (not S. murchisonianus de Koninck, 1843). 

 Spirifer arrectus Hall, 1859, Nat. Hist. N. Y., Pal., vol. iii, p. 422, pi. xcvii, 



figs, la-lh, 2a-2i, p. 430, 1861. 

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



pi. vi, figs. 26-30. 

 Spirifer murchisoni Weller, 1903, Geol. Surv. N. J., Pal., vol. iii, p. 329, pi. 



xlii, fig. 26; p. 354, pi. xlviii, figs. 1-4. 



Description. — " Length three and a half centimeters; width six. Shell 

 nearly two times wider than long, the sinus smooth ; six ribs on each side. 

 Localiiy: Schoharie, ISTew York." Castelnau, 184:3. 



" Shell transverse, varying from semicircular to semielliptical ; cardinal 

 angles sometimes rounded, but often produced beyond the width of the 

 shell below. Ventral valve more or less gibbous than the opposite : beak 

 elevated and incurved ; the area above the medium height, more or less con- 

 cave, extending to the hinge extremities, separated from the exterior shell 

 by a sharply defined margin; foramen large [covered by prominent 

 deltidial plates] ; sinus varying from a depression of moderate depth with 

 curving sides and base, to a deep angular depression which elevates the 

 mesial portion of the opposite valve in an angular fold. Dorsal valve often 

 very convex in the middle and towards the front; the mesial fold often 

 abruptly elevated, and varying from a rounded to a sharply angular 

 prominence ; the beak incurved beyond the hinge-line. 



" Surface marked by from five to seven or eight plications on each side 

 of the mesial fold and sinus, which are either round or subangular and 

 more or less elevated. The entire surface is ornamented by fine closely 

 arranged concentric stria;; and these are again crossed by finer radiating 

 striae, which are more prominent on the edges of lamella?, giving to the 

 perfect shell a granulose [rather a finely striate-spinose] exterior. 



" The casts of the ventral valve, which are abundant in the sandstone, 

 show a large prominent process which is strongly defined by the impres- 

 sions of the dental lamelku : this process, which indicates the form and 

 dimensions of the muscular area, is variously striated, sometimes with a 



