966 NODULARIA 
a very well recognizable external difference, even if the inner 
one was not so noticeable. Unio douglasie Gray is also re- 
lated, but differs in its keeled anterior end and olive-green 
color.” 
NopuLARIA porRI ( Wattebled). 
Shell small, elongated, inflated, subsolid, inequilateral ; beaks 
apparently full; posterior ridge well developed, sharp, ending 
in a point about on the median line; anterior end rounded; 
base line straight, full behind the middle, from which it is 
slopingly truncate to the posterior end; outline of the dorsal 
slope curved; surface with very delicate growth lines and 
some very slight corrugations on the umbonal region and the 
dorsal slope; epidermis dark brown, shining; pseudocardinals 
elevated, ragged, subcompressed, granular and somewhat den- 
ticulate; laterals nearly straight; beak cavities rather deep; 
muscle scars impressed; nacre bluish, sometimes yellowish in 
the cavity, thinner and brilliantly iridescent behind. 
Length 36, height 15, diam. 13 mm. 
Cochin China; Anam; Mekong River; Tonquin. 
Unio dorrt WATTEBLED, Jl. de Conch., XXXIV, 1886, p. 71, 
plw, ne. 5: 
Nodularia dorri Simpson, Syn., 1900, p. 809.—Haas, Con. 
Cab., Unio, 1910, p. 81, pl) vin, figs. 15 2! 
Close to forms of N. douglasie, but very much smaller, hav- 
ing a more sharp and elevated posterior ridge and brighter 
iacre: 
NODULARIA DENSERUGATA Haas. 
“Shell elongate-elliptical, rather solid and inflated, rounded 
in front. distinctly biangulate behind. Posterior ridge rather 
high, rounded. Basal margin almost straight. Beaks not prom- 
inent, situated at 26-100 of the total length, greatly eroded; 
their sculpture covers the greater part of the disk and consists 
of concentrical, wavy wrinkles standing very close. Epidermis 
of a dull blackish gray. Hinge consisting of two cardinals and 
two laterals in the left, one cardinal and one lateral in the 
