FOSSILS OF THE CLINTON GROUP. 567 



diverge strongly at first, and then are almost parallel along the sides, in- 

 curving again strongly along the anterior margin where they become 

 indistinct before meeting. This gives a strongly quadratic appearance 

 to the muscular area. In other words the muscular area of the pedicle 

 valve of Ohio specimens is distinctly elongate. A. fine median striation 

 divides the muscular area; it disappears anteriorly. The adductor mus- 

 cular impressions lying on either side of it are narrow. Lateral branches 

 of the median striation, which start out some distance anterior to the 

 hinge area, and curve almost directly forwards, making a low angle with 

 the median striation, define the posterior and lateral part of the adductor 

 impressions, but disappear anteriorly in one specimen, while in another 

 they become once more distinct anteriorly at the median line which here 

 is again a raised striation. 



The cardinal process of the brachial valve is so strongly divided 

 anteriorly as to appear like two strongly diverging teeth, fastened to the 

 lower side of the valve. A foraminal opening appears in one specimen at the 

 beak, where two divisions of the cardinal process meet. Two, much 

 lower, and more diverging ridges, twice as long as the divisions of the 

 cardinal process, and occupying the outer angle between these divisions 

 and the hinge area, represent the crural plates. The muscular area does 

 not show distinct impressions in the meagre material so far found. 



This species occurs in the upper shaly courses at Soldiers' Home, 

 Huffman's, Centerville, Fauver's, Beavertown; in the middle limestone at 

 Soldiers' Home, moderate; Huffman's, rare; Brown's, common; Todd's 

 Fork. In the upper courses of limestone at Brown's Quarry. 



Strop homena ( Orthothetes) Hanover ensis, Foerste. 



( Plate 31, Fig. 1 ; Plate 27, Fig. 34.) 



Since the publication of this species but little new material has 

 been added to our collections. What is regarded as the brachial valve 

 is strongly convex in mature shells, although the degree of convexity 

 varies considerably in different shells, especially if extreme forms are 

 compared; moreover, the point of greatest curvature or highest eleva- 

 tion of this valve varies considerably. In a specimen in the cabinet of 

 the Ohio State University this valve is very evenly convex, whereas, as 

 a rule, there is a region of greatest convexity which may lie nearer the 

 beak, usually within 8 mm. of the same, or which rarely lies nearer the 

 anterior margin. In the latter case the greater anterior curvature is 

 due to the presence of larger wrinkles of growth, these wrinkles of growth 

 being not infrequent in this valve, although entirely absent in some 

 specimens, as for instance in the above mentioned cabinet specimen. 

 These brachial valves are quite common. Ridiculous as it may sound 

 to others who have not worked in our western Clinton limestones, it 

 was at first impossible to determine with confidence the character of the 



