FOSSILS OF THE CLINTON GROUP. 581 



not be traced in the material examined. The shell structure is compact 

 and finely fibrous without punctation. 



The detailed description just given is drawn from specimens desig- 

 nated in an earlier publication as the variety reversata (Plate 25, Fig. 7),. 

 established to contain forms which have usually an odd number of plica- 

 tions on the median fold and an even number in the sinus, and in which 

 plications are intercalated with more than usual frequency, conspicuously 

 so in the sinus and on the mesial fold. It occurs in Ohio, in the upper 

 shaly courses at the Soldiers' Home, Fauver's, 'Huffman's, in the quarry 

 just north of Beavertown ; Centerville quarries in the shaly Clinton ; at 

 Reed's Hill in the limestone; at Huffman's in the Beavertown marl; also 

 in the Clinton of New York at Lockport. A smaller form was designated 

 as variety Dayto?iensis (Plate 25, Fig. 8). This has usually much 

 fewer striations; it occurs in the solid limestone of the Clinton at Soldiers' 

 Home, near Dayton, Ohio, quarry in John Glaser's woods five and a third 

 miles from Dayton on Brandt pike, Hanover, Indiana, L,ockport, New York, 

 and at Cumberland Gap, Tennessee, Collinsville, Alabama, and elsewhere 

 extending also into the Niagara. The markings of the interior of the 

 shells valves of this species are but little known. It is probably also 

 represented at Brown's Quarry. 



Orthis (Dalmanella) elegantula, Dalman. 



( Plate 25, Fij>e. 11, a b ; Figs. 17, a, b.) 



Brachial valve flatfish or moderately convex, with a median sinus or 

 line of depression, fairly distinct near the beak, but widening and usually 

 becoming less distinct anteriorly, at least as regards its lateral bounda- 

 ries. Pedicle valve strongly convex, especially towards the beak along 

 the median area of the shell. Both valves are marked by rather 

 fine, frequent radiating plications. With the aid of a lense, the surface 

 of the shell is seen to be further ornamented by fine little granular mark- 

 ings. These apparent granules are arranged much as these described in 

 the case of Orthis biforata. They are namely arranged more or less in 

 rows, these intersecting each other so as to give rise to a sort of quin- 

 cuncial disposition of the granules, though this may not be apparent 

 where the granules are more irregularly arranged. In worn shells it can 

 frequently be seen that these granules open below into very fine tubes, 

 entering the substance of the shell. Whether they are closed above could 

 not be determined in even the best preserved specimens, but it is not im- 

 possible that the supposed granules represent only the broken off bases 

 of very fine, hollow, hairlike spines, which once ornamented the shell, 

 and connected with the fine tubes which give the poriferous structure to 

 the worn shell. Hinge area of the valves very unequally developed, 

 that of the brachial valve usually very low, and inclined outward, while 

 the area of the pedicle valve is much higher, being erect and somewhat 



