May, 1917] Silurian Fossils from Ohio 245 



.brachials become rapidly smaller, and the third and following pairs 

 arc conspicuously smaller than the rest. Length of largest specimen 

 here figured, 66 millimeters; lateral diameter at top of calyx, 30 milli- 

 meters; antero-postcrior diameter, 23 millimeters; specimen probably 

 compressed in a direction from front to rear. 



Cedarville dolomite, at the eastern Mills quarry, a mile 

 southwest of Springfield, Ohio. 



Dalmanella springfieldensis, sp. nov. Plate XI, Figs. 5A-E. 



Pedicel vah'e strongh' convex, the convexity equalling from five- 

 tenths to six-tenths of the width in the more convex specimens. The 

 beak is strongly incurved. Some of the specimens tend to be angiilate 

 along the median line, but this is not a constant feature. Specimens 

 rarely exceed 12 millimeters in length. Casts of the interior indicate 

 the presence of strong dental lamellae, which extend forward from the 

 hinge-line for a distance of two to two and a half millimeters. 



Brachial valve only moderately convex or comparatively fiat and 

 with the greater convexity about one-third of the length of the valve 

 froin the beak; depressed along the median line. Length varying 

 from slightly less to slightly more than the width. Casts of the interior 

 indicate the presence of a small and narrow cardinal process, of strong 

 crural processes, and, in mature specimens, of strongly defined muscular 

 impressions. The median elevation separating the muscular impres- 

 sions is strongly defined, especially posteriorly where it separates the 

 posterior adductor impressions. The anterior adductor impressions 

 are not strongly differentiated from the posterior impressions, nor are 

 they strongly limited anteriorly, but laterally both sets of impressions 

 are clearly defined. 



Surface inarked by narrow radiating striae, about 5 to 6, sometimes 

 7 occurring in a width of 2 millimeters. 



From the Cedarville dolomite, at the eastern Mills quarry, 

 southwest of Springfield, Ohio. 



This species is characterized by its small size, the great con- 

 vexity of its pedicel valve, and the tendency toward elongation 

 of the latter. The second specimen figured by Nettelroth 

 (Kentucky Fossil Shells, 1889, PI. 32, Figs. 55, 56, 57) from the 

 Louisville limestone of Kentucky, evidently is closely similar, 

 and the first figured specimen (Ibid., Figs. 52, 53, 54) illustrates 

 one of the less elongated specimens of the same species. 



Dalmanella elegantula, Dalman, (Kongl. Svenska Vet.-Akad. 

 Handl., 1828, p. 117, PL 2, Figs. 6 a-g) is a much more tri- 

 angular shell. For the Waldron shale species, so well figured 

 by Hall (28th Rep. New York State Mus. Nat. Hist., 1879, 

 P. 150, PL 21, Figs. 11-17) the term Dalmanella waldronensis is 

 here proposed. 



