MARYLAND GEOLOGICAL SURVEY 603 



Dimensions. Altitude 8 mm, latitude 7.75 mm., semi-diameter, 2 mm. 



Type Locality. Brightseat, Prince George's County. 



This species differs from its near relative, L. reticulata Lyell and Forbes, 

 in the somewhat smaller size, the much more angular costse, the absence 

 of any trace of concentric sculpture upon the medial portion of the disk 

 and the development of occasional secondaries. 



Occurrence. MONMOUTH FORMATION. Brightseat and MclSTeys Cor- 

 ners, Prince George's County. 



Collection. Maryland Geological Survey. 



LIMA OBLIQUA n. sp. 

 Plate XXXIV, Fig. 11 



Description. Shell of moderate size for the group, very thin and 

 fragile, inequilateral, ovate in outline, obliquely produced along the 

 diagonal from the umbones to the anterior ventral margin ; posterior por- 

 tion of the shell compressed and obtusely rounded at the junction of the 

 dorsal lateral and the lateral ventral margins ; maximum inflation in the 

 umbonal region and along the dorsal half of the diagonal ; umbones acute, 

 obliquely compressed, somewhat posterior in position; posterior auricle 

 obsolete, the anterior very large, fully one-third as wide as the entire .shell, 

 its submargin deeply impressed and sharply differentiated from the disk ; 

 external surface sculptured with some twenty-six low, flattened radial 

 costse which tend to diastomose posteriorly; intercalations occasionally 

 developed near the ventral margin ; intercostal areas shallow, not quite so 

 wide as the costals, radial sculpture absent upon the auricle, excepting for 

 two or three very faint threadlets upon the extreme posterior portion; 

 concentric sculpture absent, excepting for very faint striations upon the 

 disk ; byssal sinus probably very shallow ; characters of hinge and interior 

 not known ; ventral margin minutely crenated by the ribbing. 



Dimensions. Altitude 11 mm., latitude 8.5 mm., semi-diameter 

 2.5 mm. 



This species is described from two imperfect specimens, but the char- 

 acters preserved are so peculiar and so diagnostic that the form lias 



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