BRACHIOPODA. 107 



1867. Cyrtina hamiltonensis Hall, Pal. N. Y., IV, pt. 1, p. 268, pi. 27, figs. 1-4; pi. 44, 

 figs. 26-33, 38-52. 



1868. Cyrtina hamiltonensis Meek, Trans. Chicago Acad. Sci., I, pt. 1, pp. 99-100, pi. 

 14, figs. 5, 7?, 10. 



1889. Cyrtina hamiltoniae Nettleroth, Kentucky Fossil Shells, Mon. Kentucky Geol. 



Survey, p. 96, pi. 13, figs. 4-12. 

 1889. Cyrtina hamiltonensis Miller, North American Geol. Pal., p. 343, fig. 558. 

 1891. Cyrtina hamiltonensis Keyes, Johns Hopkins Univ. Circ, XI, p. 29. 

 1891, 1892. Cyrtina Hamiltonensis Whiteaves, Cont. to Canadian Pal., I, pt. 3, pp. 



226-227, pt. 4, p. 288. 

 1894. Cyrtina Hamiltonensis Hall and Clarke, Pal. N. Y. VIII, pt. 2, p. 46, pi. 28, 



figs. 23-33, 43, 45, 46, 53. 



1896. Cyrtina hamiltonensis Kindle, Bull. American Pal., 6, p. 35. 



1897. Cyrtina hamiltonensis Schuchert, Bull. U. S. Geol. Surv. 87, p. 198. 

 1903. Cyrtina hamiltonensis Clarke, N. Y. State Mus., Bull. 65, p. 224. 



1909. Cyrtina hamiltonensis Grabau and Shinier, North American Index Fossils, I, 

 p. 313, figs. 393 a-c. 



1911. Cyrtina hamiltonensis Cleland, Wisconsin Geol. Nat. Hist. Surv., Bull. 21, p. 

 75, pi. 15, figs. 7-10. 



1912. Cyrtina hamiltonensis Kindle, Bull. U. S. Geol. Surv., 508, p. 81, pi. 5, fig. 4. 



1913. Cyrtina hamiltonensis Prosser and Kindle, Maryland Geol. Survey, Middle and 

 Upper Devonian, pp. 185-187, pi. 17, figs. 1-9; Clarke and Swartz, pp. 591-592, 

 pi. 56, figs. 1-3. 



Hall's description — "Shell more or less triangular-subpyramidal; hinge line equal to 

 the greatest width of the shell; proportions of length, breadth and height variable, but 

 frequently the width is equal to the length of the ventral valve, and the height of area 

 is equal to the length of the dorsal valve; surface plicate. 



Ventral valve quadrilateral in outline, obliquely subpyramidal, most prominent 

 at the break, which is very variable in elevation and straight or a little arched over the 

 area, and not infrequently attenuate and distorted or turned to one side; mesial sinus 

 wide and strongly defined, rounded or subangular in the bottom; area variable, large and 

 elevated, plane or arcuate in different degrees with the lateral margins angular, distinctly 

 striate in both directions; fissure narrow, closed by a convex pseudo-deltidium, which is 

 perforated above by an oval or narrowly ovate foramen. 



Dorsal valve depressed-convex, with a broad more or less prominent mesial fold, 

 which is bounded by broader furrows than those between the plications ; and is sometimes 

 extremely elevated in front; beak scarcely rising above the hinge line; area narrow 

 linear, but quite distinct. 



Surface marked by about six to eight (rarely one or two more) simple rounded 

 plications on either side of the mesial fold and sinus, and these are crossed by very fine 

 concentric lines of growth, which at intervals become crowded and subimbricate, es- 

 pecially towards the margins of older shells. The finer surface-marking is minutely 

 granulose or papillose, and the shell-structure distinctly punctate. In some of the larger 

 individuals there is an obscure elevation on each slope of the sinus, resembling an obso- 

 lete plication. 



The longitudinal median septum extends for more than half the length of the ventral 

 valve, and is continued into the cavity beneath the pseudo-deltidium. These features 

 are shown in the casts and in transverse sections of the valve. The dorsal valve shows a 

 double or bilobed cardinal process, with the strong crural bases supporting spiral arms, 

 which are directed into the two compartments of the ventral valve, and, making numer 

 ous turns, terminate in the rostral part of the shell." 



Remarks — The species is common in the- Mineola and, though good specimens are 

 rare, a few beautifully preserved ones have been collected. Most of the specimens are 



