Maryland Geological Survey 359 



nmbonal region prominent, and in the left valve gibbous; ear small, 

 separated from the valve by a broad sulcus, beyond which it is a mere fold 

 in the shell ; wing large, triangular, flat, extending nearly to the margin 

 of the valve, limited by a somewhat distinct sulcus and the abrupt bend- 

 ing of the concentric striae; margin concave. Test thick; left valve 

 marked with strong, prominent, rounded radii, regiilarly alternating with 

 finer ones on the posterior half of the valve; crossed at regular intervals 

 by strong concentric lamellae which generally interrupt the radii; on the 

 right valve the markings are much subdued, the rays often obsolete, espe- 

 cially on its lower part, and the concentric lamellae are simple undulations 

 of the surface; from maceration or exfoliation these surface characters 

 are usually only partially preserved. 



A number of rather imperfectly preserved impressions of this species 

 were found in the rather coarse arenaceous shales and sandstones of the 

 Maryland Hamilton. They possess the distinctive specific characters in 

 the extreme obliquity of the body; large, triangular wing; small ear, 

 separated from valve by broad sulcus ; rounded radii, with smaller ones 

 between, interrupted by prominent concentric lamellae. The specimens 

 are too imperfect for satisfactory measurements. 



Occurrence. — Eomney Formation, Hamilton Member. B. & 0. 

 E. E. cut at 21st Bridge ( ?) ; east bank Evitts Creek below Wolfe Mill; 

 on road east of Pine Hill about 4 miles north of Oldtown. 



Collections. — Maryland Geological Survey; New York State Museum; 

 American Museum of Natural History. 



ACTINOPTERIA BOYDI WAR. GIBBOSA n. Var, 



Plate XXX, Figs. 9, 10 



Description. — Shell of medium size, with straight hinge-line and some- 

 what rounded anterior and front margins. Eight valve moderately convex 

 and left valve strongly convex and gibbous along the umbonal ridge ; ear 

 short and limited by a sulcus which is more sharply defined on the left 

 valve; wing not distinctly separated from the body of the shell. Left 

 valve marked by numerous, strong, simple rays which extend from the 



