448 Trans. Acad. Set. of St. Louis. 



MOLLUSC A. 

 PELECYPODA. 



Ndcula glenparkensis n. sp. 



PlaU2,fig8.1-3. 



DescHption. Shell small, triangular-subovate in outline, 

 width about five-sixths the length, beaks of the two valves 

 closely approximate or in contact above the hinge-line and 

 situated one-fourth the length of the shell from the anterior 

 extremity. The cardinal margins sloping away from the 

 beaks anteriorly and posteriorly with an angle of about 105 

 degrees; posterior margin sharply rounded or subangular, 

 ventral margin convex and curving regularly into the rounded 

 anterior margin. Valves strongly convex, gibbous in the um- 

 bonal region, umbonal ridge not defined. Surface marked 

 with fine concentric lines which are frequently nearly obsolete 

 so that the shells appear to be smooth until examined with 

 a magnifying glass. 



The dimensions of two complete specimens are: length 6.5 

 and 6 mm., width 5.5 and 5 mm.; thickness through both 

 valves 4 and 3.5 mm. The dimensions of one of the largest 

 specimens observed, a left valve, are: length 9 mm., width 

 7.5 mm., convexity 3 mm. 



Remarks. This species resembles JSf. corhuliformis Hall, 

 but is smaller, with the beaks situated farther forward and 

 with less conspicuous concentric markings. Of the Missis- 

 sippian species of the genus it is perhaps more closely allied 

 to N. shumardana of the Spergen Hill fauna, but the beaks 

 of that species are much more anterior in position. 



NUCULANA DIVER80IDE8 U. Sp. 

 Plate 2, flga. 4-5. 



Description. Shell small, elongate-subovate in outline, 

 sub-cuneate behind, the width a little more than one-half the 

 length. Beaks prominent, incurved above the hinge-line, sit- 

 uated about one-third the length of the shell from the an- 

 terior extremity. Cardinal margin slightly convex from the 

 beak anteriorly, and concave posteriorly to the posterior 



