22 A CONTRIBUTIOX TO THE LOWEE DeVOXIAN FaUXAS OF MaRYLAXD 



To this species is referred, doubtfully, a single fragmentary individual. 

 Occurrence. — Oeiskaxy Formatiox. Locality unknown. 

 Collection. — Eobert H. Gordon. 



Section ISODONTA 

 Family PECTINIDAE 



Genus AVICULOPECTEN McCoy 

 AVICULOPECTEX ( ? ) CDMBEBLAX'DEXSIS n. sp. 



Plate LXXVIII, Fig. 3 



Description. — Shell subcircular, length and height about equal ; slightly 

 oblique; left valve gibbous, the maximum inflation being anterior to the 

 center of the shell which curves thence steeply to the anterior, and much 

 less so to the basal and posterior margins ; anterior margins broadly sinuate 

 at junction of anterior wing and the body of the shell, thence slightly 

 convex outward to anterior extremity, thence the margin is almost semi- 

 circular to the posterior wing which is widely sinuate, the maximum ex- 

 cavation being at about two-thirds the distance from the extremity of the 

 wing to the body of the slieil ; anterior wing small, concave ; posterior wing 

 large, convex, the extremity being nearly a right angle and on line with 

 the posterior extremity of the body; hinge-line straight, equal to greatest 

 width of shell. Surface of body ornamented with coarse, radiating ribs 

 which are subequal on the anterior, and alternating on the central and 

 posterior parts; the radiating ribs are crossed l\v finer concentric striae 

 and irregular growth lines; surface of posterior wing ornamented with 

 alternating ribs which are somewhat finer than those of the body and 

 crossed by concentric stria?, the two sets of markings giving a cancellated 

 effect. 



Eight valve and interior not seen. The description is from a single left 

 valve, which is figured. The label has been lost but the specimen is no 

 doubt from the Helderberg, as is shown h\ other fossils in the rock mass. 



Length about 5 cm. ; height 5.2 cm. 



Occurrence. — Helderberg Forimatigx. Locality unknown. 



Collection. — Marvland Geological Survev. 



