230 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 46. 



UNIO (PLEUROBEMA?) ALEXUS, new species. 

 Plate 20, fig. 2. 



Shell represented by a fragment which from the incremental lines 

 must have been a shorter, heavier, and more triangular shell than 

 U. sandrius, the beaks are nearly terminal and, though decorticated, 

 show a median depression but no traces of concentric sculpture; the 

 ligamentary area is impressed much as in U. sandrius, but is much 

 shorter, wider, and more triangular; the tooth above is divided into 

 two laminae, transversely corrugated and narrow as seen from above, 

 but below is very thick and ponderous and deeply raggedly cleft for 

 the opposite cardinal. There is one left lateral and sulcus as in the 

 last, but shorter. The proportions, taken from incremental Imes, are 

 length 16, height 11, diameter about 10.5 mm. The adult shell of 

 course was at least twice that size. 



Same locality (station 6040) as the last species, from which it 

 differs in form, in weight, and especially in the character of the 

 ligamentary area and left cardinal tooth. Type, U. S. Nat. Mus., 

 No. 166289. 



It might perhaps be regarded as nearest to Pleurohema clava of the 

 recent fauna. 



UNIO (UNIO) MUSIUS, new species. 

 Plate 20, fig. 6. 



Shell short, rounded-triangular, represented by a fragment in- 

 cludmg the perfect umbo of a right valve; ligamentary area narrow, 

 elongate, two rather thickish right laterals, the cardinal strong, tri- 

 angular with the upper surface deeply transversely strigose; there is 

 a faintly elevated ray from the beak which has six or seven subequi- 

 distant concentric lamellae, strongest behind and somewhat produced 

 when they cross the ray; on the anterior umbonal slope two or three 

 elevated threads arise in a radiating manner; becommg more prom- 

 inent distally. 



Length of fragment about 11 mm. Type, U. S. Nat. Mus., No. 

 166290. 



This appears to resemble U. obesus hlandingianus of the recent 

 fauna; it comes from the same locality (station 6040) as the pre- 

 ceding species, from which it is obviously very distinct. 



OSTREA VIRGINICA Gmelin. 



Ostrea virginica Gmelin, Syst. Nat., p. 3336, 1792. 



Ostrea elongata Solander, Portland Cat. No. 3312, p. 151, 1786. 



Stations 3614, 6040, 6440, and 6445. Also Pliocene of Florida, 

 Pleistocene, and Recent. 



The only stations from which identifiable oysters were obtained 

 were 3614 and 6440, in Texas. But abundance of comminuted frag- 

 ments and very young valves occurred at all the stations. 



