May, l\)it\ Silitriaii Fossils from Ohio 249 



flat, or is occupied by a single, almost obsolete, low, broad 

 plication. Two thin dental plates extend forward from the 

 beak for a distance of 6 mm. Where they rest on the interior of 

 the valve, they form an angle of about 30 degrees with each 

 other. Midway between them there is a low but thin and sharp 

 median ridge, as in some species of Spirifer, and the general 

 aspect of these pedicel valves is spiriferoid. In this respect 

 they differ from the ventral valve of the type of Stricklandinia 

 louisviUensis, so that it is possible that the pedicel valves are 

 even generically distinct from the brachial valves described 

 above, notwithstanding their general resemblance. (Figs. 7 

 A, B, on plate XII.) 



Dictyonella reticulata, Hall. Plate X. Figs. 4A, B. 



The first published figures of Dictyonella reticulata, from the 

 Waldron shale, at Waldron, Indiana, occur in the Twentieth 

 Report on the New York State Cabinet of Natural History, 

 page 275, 1867. Here Figures 1 and 2 indicate the presence, on 

 the brachial valve, of a median fold distinctly defined from the 

 beak to the anterior margin, the sides of the fold forming an 

 angle of 30 degrees. These figures are reproduced in the Elev- 

 enth Report on the Geology and Natural History of Indiana, 

 1881, where they form Figures 53 and 54 on Plate 26. An 

 examination of the series of type specimens, preserved in the 

 American Museum of Natural History, and there numbered 

 1,944, indicates the presence of four individuals, including all of 

 those figured in the Indiana report. In none of these is the 

 median fold as distinctly defined as indicated in the figures 

 mentioned above; in fact, it is readily distinguished only under 

 cross illumination, and then only anteriorly, the posterior part, 

 toward the beak, being almost obsolete. Moreover, the angle 

 made by the sides of the median fold, if the lateral slopes of the 

 latter be included, is nearer 35 degrees. The specimen first 

 figured by Hall, regarded as the type of the species, is illustrated 

 in the present publication by Figure 7 on Plate XL 



In Dictyonella corallifera, Hall, figured on Plate 58, of the 

 second volume of the Paleontology of New York, from the 

 Rochester shale of New York, both the median fold on the 

 brachial valve and the corresponding sinus on the pedicel valve 

 are distinctly defined from the beak to the anterior margin. 



