570 GEOLOGY OF OHIO. 



than usUal. The species occurs also near Dayton; at Soldiers' Home, also 

 at Fair Haven, Centerville, Ohio, and at Hanover,, Indiana. 



At Hanover, Indiana, and at Soldiers' Home, Ohio, occur specimens 

 which look like sickly specimens of Str. patenta, in which the radiating 

 striae are rather large for this species, and the shell is decidedly flattened, 

 so that in the brachial valve for instance the part anteriof to the usually 

 more or less geniculate bending of the shell is but moderately depressed 

 below the general surface of the shell, and in the case of a large Soldiers' 

 Home specimen, 28 mm. long, the curvature was reversed a second time 

 within 4 mm. of the margin, the shell becoming quite concave; so that in 

 this specimen the brachial valve was plainly concave near the beak, turning 

 to moderately but distinctly convex at 14 mm. from the beak, and it again 

 became concave at 25 mm, from the beak. In these sickly forms there is 

 a tendency to an obscure irregular mesial fold, owing to the general flat- 

 tening of the shell. A careful examination of the specimens precludes 

 the idea that these peculiar specimens could be due to pressure acting upon 

 the ordinary Str. patew,ta. 



Orthis (Orthis-Dinorthis) calligramma, Dalman. 



(Plate 25,Figs. 12, a, b; Plate 31, Figs 4,5; Plate 37a, Figs. 20 a, b var.) 



This is a very variable species, of which the extreme forms are 

 readily distinguishable, but between these are all imaginable intermedi- 

 ate stages, as a former publication (Pfoc. Boston Soc. Nat. Hist. vol. 

 XXIV, pp. 308-312, 1889) attempts to show. 



One extreme is represented by a rather large form with a moderately 

 convex brachial valve, with a shallow broad median sinus, and a strongly 

 convex pedicle valve, especially convex along its median area, towards 

 the beak, the beak itself being strongly incurved. In, this form are found 

 the, fewest and strongest radiating plications. The plications are strong 

 and rounded and are separated by grooves of breadth almost equal with 

 the plications, in exfoliated specimens apparently broader. The shell is 

 further marked by numerous much finer and closer radiating strise, and 

 by fine strise of growth, which in the specimens examined are some- 

 what less distinct than the radiating strise. Search was made for little 

 oblique openings along the middle of the plications, but nothing could 

 be accurately determined as such, although at times it was thought that 

 they could be seen in exfoliated specimens. This form finds its nearest 

 relatives with typical Orthis, as redefined by Hall and Clarke. It is 

 found at the Soldiers' Home, Fauver's and Huffman Quarries in Ohio, 

 and at Hanover, Indiana. (Plate 25, Figs. 12 a, b.) 



The other extreme of this is represented by a form with much more 

 strongly, although still moderately, convex brachial valves and a pedicle 

 valve, which although quite strongly convex when very young, becomes 

 decidedly flattened when older. At this stage the shell begins to curve 



