140 BULLETIN 90, UNITED STATES NATIONAL MUSEUM. 



Mittrea Gray, Fig. MolL An., vol. 5, p. 35, 1857. 



ITaras Risso, Hist. Nat. Eur. Mer., vol. 4, 1826, p. 344, pi. 12, fig. 167. 



Type, T. antiquatus Risso (Tertiary). 

 Diplodonta Dall, Proc. U. S. Nat. Mus., vol. 23, No. 1237, p. 792, 1901; 



Trans. Wagner Inst., vol. 3, pt. 6, pp 1178, 1179, 1903 



DIPLODONTA ALTA Dall. 

 Plate 24, fig 8. 



Diplodonta alta Dall, Trans. Wagner Inst., vol. 3, pt. 1, p. 189. pi. 11, figs. 

 9a, 9&, 1890 (poor) ; pt. 6, p. 1183, pL 44, fig. 19 (good), 1903. 



Oligocene of the Tampa silex beds, Ballast Point, Tampa Bay; 

 of the lower bed at Alum Bluff, Chattahoochee River; and of the 

 marl of the Chipola Eiver, near the county bridge, Calhoun County, 

 Florida. U. S. Nat. Mus. No. 155745. 



The j&rst figures of this species were made from a defective speci- 

 men that was discarded in favor of a more perfect one from the 

 Chipola marl. 



DIPLODONTA CATOPOTIUM, new species. 

 Plate 18, fig. 9. 



Shell small, thin, almost spherical, smooth except for concentric 

 incremental lines, which are irregular and rude ; beaks almost central, 

 low, smooth, with hardly any trace of a lunular depression in front 

 of them and only a very narrow chink for the ligament behind them ; 

 interior inaccessible, but from what can be seen of the margins they 

 are probably entire. Height of shell 8 mm., length 8 mm., diameter 

 7 mm. 



Tampa silex beds, one specimen. U. S. Nat. Mus. No. 16G111. 



This species has much the form of D. turgid a Conrad (not Ver- 

 rill), but its beaks are lower and the impressed lunular area of D. 

 turgida is wanting. 



Section PHLYCTIDERMA Dall. 



Phlyctiderma Dall, Journ. Conch. (Leeds), vol. 9, No. 8, 1899, p. 246. Type, 

 Diplodonta semiaspcra Philippi (recent, Havana, Cuba) ; Proc. U. S. 

 Nat. Mus., vol. 23, No. 1237, p. 792, 1901. 



DIPLODONTA (PHLYCTIDERMA) PUNCTURELLA Dall. 



Diplodonta puncturella Dall, Journ. Conch. (Leeds), vol. 9, No. 8, Oct., 



1899, pp. 245-6. 

 Diplodonta ( Phlyctiderma) puncturella Dall, Trans. Wagner lust., vol. 3, 



pt. 6, p. 1183, pi. 45, fig. 26, 1903. 



Oligocene of the Bowden beds, Jamaica, West Indies, and of the 

 Tampa silex beds at Ballast Point, Tampa Bay, Florida. Recent, 

 Jamaica, Porto Rico, and St. Thomas, West Indies. U. S. Nat. Mus. 

 No. 165203. 



The punctuation of the surface of this small species is very close 

 and regular, not pustulose like most of the species of this section. 



