PROCEEDINGS OP UNITED STATES NATIONAL MUSEUM. 139 



LUCINA CLEBURNI (sp. nOV.). 

 (Plate — , Figs. 3 and 4.) 



Shell moderately large, indistinctly pentahedral in marginal ontliue; 

 valves moderately convex ; posterior side truncate, basal border rather 

 short, nearly straight or slightly convex, abruptly rounded up to the 

 posterior border and broadly rounded up to the antero-basal border; 

 front prominent, somewhat abruptly rounded above; anterodorsal bor- 

 der slightly concave, nearly horizontal; postero-dorsal border slightly 

 convex, sloping downward and backward, its whole length occupied by 

 a large prominent external ligament; lunule very narrow, hardly so 

 wide as the ligament, and extending the whole length of the antero- 

 dorsal border; beaks small, situated subcentrally ; umbonal ridge not 

 well defined, passing near the posterior and postero-dorsal borders. 

 Surface marked by the usual distinct lines of growth, and also by some- 

 what numerous strongly and sharply raised concentric lines, especially 

 upon its upper and umbonal portions. 



Length 37 millimeters; height 30 millimeters; thickness, both valves 

 together, 14 millimeters. (Museum No. 11469.) 



This fine shell bears some resemblance to the preceding, but it is a 

 more robust form, its transverse diameter is proportionally greater, the 

 front more prominent, the basal border less abruptly rounded, and the 

 external ligament larger and more prominent. In its large size it re- 

 sembles L. occidentaUs Morton, as identified by Meek and figured in 

 vol. ix, TJ. S. Geol. Sur. Terr., but in its abrupt posterior truncation and 

 greater prominence of the uj^per jiortion of the front it difiers con- 

 spicuously from that species. 



The ligament of this shell is unusually large and prominent for that 

 of a Lucina, but it has the outward characteristics of a species of that 

 genus. Besides this, an imiDerfect separate valve, too fragile for pre- 

 servation, which was found associated with the other specimens, and 

 which apparently belongs to the same species, shows the hinge, pallial 

 line, aud muscular markings which characterize Lucina. 



Position and locality. — Later Cretaceous strata (equivalent with the 

 Fox Hills and Fort Pierre Groups of the Upper Missouri River region) 

 in the vicinity of Julesburg, Colo., where it was obtained by Mr. W. 

 W. Cleburn, and in whose honor the specific name is given. 



SoLEMYA BiLix White. 



(Plate—, Fig. 9.) 

 Solemya hilix White, 1880, Proc. U. S. National Museum, vol. iii, p. 158. 



This species was also found by Mr. Celeburn, near Julesburg, Colorado. 

 Pteria (Oxytoma) erecta White. 



(Plate—, Figs. 7 and 8.) 

 Ptma {Oxytoma) erecta WMte, 1880, Proc. U. S. National Museum, vol. iii, p. 157. 



