658 GEOLOGY OF OHIO. 



name cincinnatiensis strictly applicable? The evidence afforded by the 

 description and figures is not entirely conclusive for either the one or the 

 other. One thing however may be accepted as reasonably certain, and 

 that is that the majority of the specimens so named b)^ Hall and Whit- 

 field belong to the common form. Hence, if a separation is to be made, 

 the best justified course is the elimination of the rarer form. Another 

 good reason for this course is found in the fact that Walcott proposed the 

 name Modiolopsis cancellated for what I believe to be merely a young 

 example of the latter, which he discovered in the Utica slate of New 

 York. 



Actinomya kentonensis, n. sp. 



Plate 56, Figs. 18-.0. 



Shell of medium size, moderately convex, elongate, subovate, narrow 

 anteriorly; thickness, height at beaks, greatest posterior height, and 

 length respective^ to each other as three, four and six or seven are to 

 thirteen or fourteen. Cardinal margin nearly straight or gently arcuate, 

 passing gradually into the uniformly rounded — almost semicircular — pos- 

 terior margin; basal line gentry convex behind, nearly straight in the 

 central half, on the whole, rising gradually to the short and narrowly 

 rounded anterior end. Beaks comparatively small, projecting but little 

 be3^ond the hinge line, situated about one-seventh of the length of the 

 shell behind the anterior extremity. Umbonal ridge rounded, not prom- 

 inent; mesial depression quite undefined, producing but a slight flatten- 

 ing of the umbones and of the surface of the valves beneath them. Sur- 

 face marked with rather obscure, concenti ic undulations and fine lines of 

 growth, the former showing through the shell so as to be visible on casts 

 of the interior. Two or three faint ra)'s may be observed on the poste- 

 rior half- of the umbonal ridge of casts. Anterior muscular scar rather 

 small, obovate, erect, not strongly defined ; posterior scar and pallial line 

 faint, not satisfactory observed. Test very thin. 



The position of this fine species seems to be intermediate between 

 the typical section of the genus and that other group of species of which 

 A. pholadiformis, Hall, sp., may be regarded as representative. Of de- 

 scribed species, there is none that is at all likely to be confused with A, 

 ke?itonensis , but I have illustrated two closely related forms on one of the 

 plates, which, because of a lack of room, had to be omitted from this 

 report. f One has very nearly the shape of A. pholadiformis, but is with- 

 out the peculiar surface ornamentation so characteristic of that species. 

 The obliquely truncate posterior end will distinguish it from the present 

 species. The other is more elongate and has, for so long a shell, an 

 unusually convex base. 



* 1879, Trans. Albany Insti., Vol. X, p. 22. 



tl shall endeavor to publish these platen as soon as possible, together with 

 others on Lower Silurian Avicu/idcz, the only important family of those known 

 from these early paleozoic rocks remaining to receive the semi-fin il treatmenr 

 accorded to the other families in this and the Minnesota work. 



