, PALEONTOLOGY. 471 



Genus SPIRIFERA Sowerby. 



Spirifera {Martinia) contractu. 



Plate IX, figs. 17-19. 

 Spirifera (Martinia) glabcr var. contractus M. and W., Geol. Rept. 111., vol. 2, p. 298, 

 pi. 23, fig. 5. 



Shell of medium size, broad ovate or globular in general form with highly 

 ventricose or gibbons valves, and a short hinge-line with rounded cardinal extrem- 

 ities. Ventral valve the most gibbous, with a large and strong incurved beak; car- 

 dinal area small, one-third or less than one-third as high as long, divided in the 

 centre by a rather wide fissure ; hinge-line less than half the width of the shell 

 below, the cardinal slopes strongly and abruptly rounded; centre of the valve 

 deeply impressed by a moderately wide, subangular mesial sinus. Dorsal valve 

 nearly orbicular, moderately convex from side to side; beak small, slightly tumid, 

 projecting slightly beyond the cardinal line; mesial portion somewhat strongly 

 defined at the margins, and does not extend above the middle of the shell. Sur- 

 face of the valves smooth to the naked eye, but under a magnifier is seen to be 

 marked by fine, obscure, radiating lines.and by.trausverse lines of growth. 



All the specimens seen are exfoliated to a greater or less degree, so 

 that the real surface has not been seen. The surface striae, seen by the 

 aid of a lens, are too strong and distinct not to be a surface character, as 

 they are readily felt by the hand, although not readily visible to the un- 

 assisted eye. The shell does not attain a very large size, no specimens 

 examined exceeding one and three-eighths inches in length, by a trans- 

 verse diameter of about one and one-fourth inches. The shells are 

 somewhat variable in form, being proportionally more or less elongate 

 than the measurements above given. They also differ much in the size 

 and strength of the mesial elevation and sinus, and in the length of the 

 hinge-line. I have much doubt as to the absolute identity of this shell 

 with the Illinois shells described and figured by Messrs. Meek and 

 Worthen, from the fact that these appear distinctly marked by the radi- 

 ating striae, while those from the west are said to be smooth, except for 

 the concentric lines of growth, though occasionally showing faint evi- 

 dences of obscure radiating lines. The fact that the authors of that 

 species refer it to Sp. glaber, which is entirely destitute of radiating lines, 

 would seem to indicate it as different from the Ohio forms. 



Spirifera Rockymontana f 

 Plate IX, fig. 20. 

 Spirifera Rockymontana Murcou, Geol. N. Amer., p. 50, pi. 7, fig. 4; Feb., 1858. 

 Spirifera Keokuk Hall, Geol. Rept. Iowa, vol. 1, pt. 2, p. 642, pi. 20, fig. 3 ; Sept., 1858. 

 Spirifera Keokuk var. Hall, Ibid., p. 672, pi. 24, fig. 4. 

 Spirifera opima Hall, Ibid., p. 711, pi. 28, fig. 1. 



' Several specimens of a Spirifera, of the form referred to S. Keokuk 

 var. Prof. Hall, have been obtained from Newtonville, Ohio, which are so 

 entirely similar to those from the St. Louis and Chester limestones of 

 Iowa, as to be absolutely undistinguishable ; the form of the shell, the 



