390 SYSTEMATIC FALEOXTOLOGY 



Description. — "Triangular, elongated, moderately thick, convex-de- 

 pressed; posterior side cuneiform; apex hardly oblique, subcentral; 

 fosset wide; lateral teeth transversely striated." Conrad, 1841, 



Only young specimens have been obtained in Maryland. 



Occurrence. — Choptank Formation. Governor Bun, 2 miles south 

 of Governor Run, Flag Pond, Jones Wharf, Pawpaw Point. Calvert 

 Formation. 3 miles south of Chesapeake Beach, Plum Point. 



Collections. — U. S. National Museum, Maryland Geological Survey. 



Spisula (Hemimactra ?) chesapeakensis n. sp. 

 Plate LXXI, Fig. 1. 



Description. — Shell large, thin, not inflated, subtrigonal, anterior and 

 posterior sides nearly equal, surface smooth; anterior end well rounded, 

 posterior end rather more sharply rounded ; anterior hinge line straight, 

 posterior hinge line gently convex, just posterior to the beak, otherwise 

 straight; angle between anterior and posterior hinge lines about 105°; 

 basal margin strongly curved anteriorly and posteriorly ; hinge area broad ; 

 lateral teeth prominent; chondrophore long, narrow, triangular, oblique. 



A single right valve of this magnificent species has been obtained. It 

 is in the form of a cast, with a portion of the shell substance preserved 

 and the outline and main hinge features easily distinguishable. It is 

 much larger than any of the other Miocene Spisulas ; S. suhponderosa is 

 nearest it in size, but is smaller, much heavier, more elevated, and has a 

 curved posterior hinge line and a broader, shorter chondrophore. 



I^ength, 130 mm. ; height, 95 mm. 



Occurrence. — Calvert Formation. 3 miles north of Plum Point. 



Collection. — Maryland Geological Survey. 



Genus LABIOSA (Schmidt) Moller. 

 Subgenus RAETA Gray. 



Labiosa (Raeta) sp. 



Description. — At Reed's marl pit have been found numerous fragments 

 of a Lahiosa showing an undular concentric sculpturing much stronger 

 than R. alta, in fact as strong as L. canaliculata. As this latter species 

 i-^ laiown only in the Pleistocene and Recent it is very probable that 



