200 THE DEVONIAN OF MISSOURI. 



folds on each side of the mesial sinus and elevation, which become obsolete towards the 

 beaks; concentrically marked by fine, regular, closely arranged, imbricating lamellose 

 striae."— Hall, 1859. 



Remarks — A small individual which has 3 plications on each side of the fold and 

 sinus is doubtfully referred to this species. 



Genus Spirifer Sowerby 



Spirifer cyclopterus Hall 



Plate 51, figures 12-27 

 Spirifer cycloptera Hall, 1857, 10th Ann. Rept. N. Y. State Cab. Nat. Hist., p. 58.. 

 Spirifer cyclopterus Hall, 1859, Pal. N. Y., vol. Ill, p. 199, pi. XXV, figs, la-z, 1861. 

 Spirifera cycloptera Billings, 1863, Geol. Canada, p. 957, fig. 457. 

 Spirifera cycloptera Billings, 1874, Pal. Fossils, vol. II, p. 48, pi. 3a, fig. 4. 

 Spirifera cycloptera Hall, 1883, 2nd Ann. Rept. N. Y. State Geol., pi. LXI, figs. 12, 13. 

 Spirifer cyclopterus Hall and Clarke, 1893, Pal. N. Y., vol. VIII, pt. II, p. 36, pi. XXXVI, 



figs. 12, 15, 1894. 

 Spirifer cyclopterus Girty, 1899, U. S. Geol. Surv., 19th Ann. Rept., pt. Ill, p. 565. 

 Spirifer cyclopterus Weller, 1903, Pal. N. J., vol. Ill, pp. 287, 314, pi. XXX, fig. 2; 



pi. XXXVIII, figs. 1-6. 

 Spirifer cyclopterus Clarke, 1908, N. Y. State Mus., Mem. 9, pt. 1, p. 178, pi. 32, figs. 



14-21. 

 Spirifer cyclopterus Clarke, 1909, N. Y. State Mus., Mem. 9, pt. 2, p. 84. 

 Spirifer cyclopterus Schuchert, 1913, Md. Geol. Surv., L. Dev., p. 406, pi. LXIX, figs. 



8-10. 



Description — "Shell semi-circular; extremities of the hinge line more or less sym- 

 metrically rounded. Ventral valve gibbous; beak elevated, more or less incurved; 

 sinus moderately deep, curved on the sides and nearly flat in the middle. Dorsal valve 

 very convex towards the middle, the mesial fold abruptly elevated and very prominent; 

 beak little elevated above the hinge line, and scarcely incurved. Area moderate, 

 scarcely extending to the extremity of the hinge line. Foramen large. Surface marked 

 by five to seven rounded plications on each side of the mesial line, concentrically marked 

 by fine close imbricating lamellose striae, which are more or less prominent, depending on 

 the condition of preservation in the shell; surface of lamellae ornamented by short fine 

 vertical striae or crenulations, which project in fimbriae on the edge of the lamellae. 



"[Remarks] — This species presents comparatively little variety in form; though 

 there are, rarely, to be found individuals with the cardinal extremities much extended 

 * * and others where the extremities are subangular * * * The 

 greater number, however, are rounded * * * 



" * * * The muscular impressions of the ventral valve are very deep and 



strong, the margins of the foramen terminating in prominent teeth. * * 



—Hall, 1859. 



Remarks — The Missouri specimens have the medial fold of the dorsal valve shallowly 

 depressed medially from the anterior margin posteriorly; and have from 5 to at least 8 

 plications on each side of the medial fold and sinus. 



Family Suessiidae 



Genus Cyrtina Davidson 



Cyrtina dalmani (Hall) 

 Plate 51, figures 30, 31; plate 52, figures 1-4 

 Cyrtia dalmani Hall, 1857, 10th Ann. Rept. N. Y. State Cab. Nat. Hist., p. 64. 

 Cyrtia dalmani Hall, 1859, Pal. N. Y., vol. Ill, p. 206, pi. XXIV, figs. 2a-y, 1861. 



