796 PROCEEDINGS OF THE NATIONAL MUSEUM. 



(Group of Quadrula ostreata.) 



Shell rhomboid, incurved on the base, with a well- developed posterior 

 ridge, somewhat biangulate behind; beak sculpture consisting of a 

 number of fine, concentric ridges showing a tendency to be doubly 

 looped, which gradually change, first to corrugations and then to pus- 

 tules; pseudocardiuals ragged, secondary lateral of right valve but 

 slightly developed. 



Animal unknown. 



t QUADRULA OSTREATA Morelet. 



* Unio ostreatus MORELET, Test. Noviss., No. 1, 1849, p. 29. * FISCHER and CROSSE, 



Miss. Sci., Pt. 7, II, 1894, p. 573, pi. LXIII, fig. 3; LXX, fig. 4. 



Ilio Usumacinta, Guatemala. 



t QUADRULA USUMASINT^E Crosse and Fischer. 



* Unio usumasintw CROSSE and FISCHER, J. do Conch., XL, 1892, p. 294. * FISCHER 



and CROSSE, Miss. Sci., Pt. 7, II, 1894, p. 574, pi. LXIII, fig. 4; LXVII, fig. 5. 



Rio Usumacinta, Guatemala. 



t QUADRULA GUATEMALENSIS Simpson. 



* Quadrula gnatemalensis, SIMPSON, Pr. Acad. N. Sci. Phila., 1900, p. 83, pi. n, tig. 4. 



Rio Usumacinta, Guatemala. 



(Group of Quadrula percompressa.) 



Shell large, triangular to rhomboid, greatly compressed throughout, 

 with a low posterior ridge and a slight secondary ridge above it, mak- 

 ing the shell slightly biangulate posteriorly; beaks very prominent, flat- 

 tened; beak sculpture not seen; surface of the disks covered with 

 rather fine, somewhat lachrymose nodules, corrugate wrinkled on the 

 posterior slope; 1 cavity of the beaks enormously deep and compressed; 

 area outside the palleal line wide in front; shell thickened anteriorly. 



t QUADRULA PERCOMPRESSA von Martens. 



* Unio percomjiressus VON MARTENS, Sitzunga Ber. Nat. Tr. 1887, p. 107. 



* FISCHER and CROSSE, Miss. Sci., Pt. 7, II, 1894, p. 576; Biologia Cent-Am. 

 Mollusca, 1900, p: 496, pi. xxxn, figs. 1-3. 



Rio de las Salinas, Guatemala. 



Subgenus LAMPROTTILA Simpson, 1900. 

 (Type, Chama plumbea Chemnitz.) 



Shell rounded to triangular, inflated, with high beaks; beak sculpture 

 consisting of a few coarse, subparallel ridges which are slightly doubly 



1 Only two left valves of this remarkable species have been seen by the writer, 

 both of which curve to the left in front and to the right behind. It is probable that 

 others may turn to the right, and von Martens' shells are fiat. 



