19-4 Systematic PALEOXTOLOciY — ]\riDDLE Devonian' 



Spirifer acuminatus Clarke, 1903, N. Y. State Mus., Bull. 65, p. 308. 

 Spirifer acuminatus Grabau and Shimer, 1909, N. Am. Index Fossils, vol. i, 

 p. 326, fig. 414. 



Dcscripiion. — Sliell large, ventricose; hinge-line nsualh^ less than the 

 width of the shell ; cardinal extremities roimded or trimcate. Ventral 

 not so convex as dorsal valve; wide mesial sinus which is well defined in 

 the npper part, becomes wider, deeper and less distinctly defined in the 

 middle of the shell and is greatly produced in front. Dorsal valve gib- 

 bous, highly <>levated in the middle into a sharply angular mesial fold 

 and curving from the sides of the fold to the margins of the shell, except 

 at the cardinal angles, where it is a little flattened. Surface marked by 

 from sixteen to twenty plications on each side of the fold and sinus, 

 three or four of which nearest the center are deeply grooved to dichoto- 

 mous from below tlie middle of their length; the first ten or twelve 

 plications on each side of the center cover the greater part of the valve. 



This species is rare in JMaryland and in the Johns Hopkins Collection 

 is represented by a single broken internal impression of the dorsal valve. 

 There is, however, apparently no doubt regarding its identity for the 

 sharp angular fold and central dichotomous plications are well shown. 

 Hall mentioned an impression of this species in the Museum of Marietta 

 College, Ohio, which he stated " from its character, has been derived 

 from the southwestern extension of the Hamilton group, perhaps in Vir- 

 ginia '' ;' and Keyes listed it in his paper on the " Paleozoic fossils of 

 Maryland." ^ This species is easily distinguished from the other Spir- 

 ifers by the high, sharply angular mesial fold and deep sinus, with the 

 few dichotomous plications on each side. 



Length, 30 mm. : width, 36 mm., and a comparison of figures indi- 

 cates that the proportions are about as five to six. 



Occurrence. — T'omney Formation, HAiiiLTONT Member. ]\IcCoys 

 Ferry. 



Collections. — Maryland Geological Survey; New York State ]\Iuseura; 

 American Museum of Natural History. 



» Pal. N. Y., vol. iv, p. 202. 



-Johns Hopkins Univ. Circ, vol. xi, p. 29. 



