COAL-MEASUKE SPECIES. 331 



the right valve; beaks compressed, scarcely projecting above the car- 

 dinal margin, and placed a little behind the middle of the hinge, as 

 well as that of the valves. Surface of both valves elegantly ornamented 

 by numerous, sometimes sharply elevated, nearly equal, very regularly 

 arranged radiating and concentric lines, which are larger and more 

 strongly defined on the anterior ear of the right valve, particularly the 

 radiating markings, which there sometimes assume the character of 

 small costse, while the concentric markings there in some examples pro- 

 ject as little lamellae slightly above the hinge margin, so as to give it a 

 subdented appearance. 



Height of one of the largest specimens seen, 1.32 inches ; antero-pos- 

 terior diameter, 1.20 inches; convexity, about 0.18 inch. 



I know of no other shell in our rocks that is liable to be confounded 

 with this, its general form and neatly cancellated markings being suffi- 

 cient to distinguish it. Although I refer it provisionally to Aviculopecten, 

 I really do not think it belongs properly to that genus, as restricted to 

 the typical forms. At least it differs from all the characteristic forms 

 of Aviculopecten in having the anterior ear larger than the posterior, as 

 well as in having its beaks placed a little behind the middle of the 

 valves, thus giving the slight backward obliquity mentioned in the 

 description. This latter character seems to approximate it to Streblop- 

 teria of McCoy, but as we know nothing of its hinge and iiiterior, it is 

 not possible to determine whether it belongs to that group or not. 



The specific name is given in honor of the Rev. H. Hertzer, of the 

 Ohio Geological Survey, to whom I am indebted for the use of some fine 

 specimens from his own private collection. 



Locality and position : Newark, Ohio. Lower Coal Measures. 



Genus PLACU]S"0PSIS, Morris and Lycett, 1853. 

 [Monogr. Fossils Great Oolite, 6.] 



Placunopsis eecticaedinalis, Meek. 



Plate 19, fig. 12. 



Shell truncato-suboval or subquadrilateral, slightly oblique, with length 

 and breadth nearly equal ; cardinal margin straight, not quite equaling 

 the greatest breadth of the valves ; lateral margins almost straight and 

 parallel, meeting the hinge at nearly right angles, and rounding regu- 

 larly to the rounded ventral edge ; upper valve depressed, most convex 



