Maryland Geological Survey 521 



Collection. — Maryland Geological Survey. 



Outside Distribution. — Monmouth. Formation. Navesink marl, New 

 Jersey. Ripley Formation. Hardeman County, Tennessee. 



YOLDIA NOXONTOWNENSIS n. sp. 



Plate XIX, Fig. 14 



Description. — Shell approximately equivalved, inequilateral, elongate, 

 transversely ovate in outline, moderately inflated in the umbonal region, 

 flattening distally and toward the base ; umbones rather tumid, opistho- 

 gyrate, slightly anterior in position; umbonal angle 145° to 150°, anterior 

 dorsal slope higher than the posterior, anterior lateral margin rounding 

 evenly into the base; shell produced posteriorly, obscurely rostrate and 

 distally truncate; base line asymmetrically arcuate, obliquely ascending 

 behind ; external sculpture not known ; hinge taxodont, teeth V-shaped, 

 acutely angulated, closely crowded, arranged in two discrete series, prob- 

 ably about twelve in the anterior and fifteen in the posterior series ; muscle 

 impressions and sinus not observed. 



Dimensions. — Altitude 8 mm.; latitude 18 mm.; semi-diameter 3 mm. 



The species is allied apparently to Y. protexta (Conrad), but is more 

 inflated in the umbonal region and relatively higher and less produced 

 both anteriorly and posteriorly. It is only after long hesitation that a 

 species founded on material so imperfect is given a place in the nomen- 

 clature. 



The greensand at Noxontown Pond has yielded a most baffling fauna. 

 The fossils are exceedingly prolific, but so ill-preserved that even good 

 casts can be obtained only with the greatest difficulty. The horizon is 

 higher than any in Maryland and is possibly synchronous with the Kan- 

 cocas of New Jersey, although there are a number of peculiar forms at 

 both localities. It seems most unfortunate that such a fauna must be 

 either disregarded or inadequately introduced. 



Occurrence. — Rancocas Formation'. South feeder Noxontown Pond, 

 Delaware. 



Collection. — Maryland Geological Survey. 



