THE NATURAL HISTORY SURVEY. sh 
parallel ridges, which usually nearly follow the growth lines, 
but sometimes become somewhat double looped with fine radi- 
ating ridges behind the beaks and often in front of them; hinge 
teeth imperfect; one large, curved, compressed, irregular cardi- 
nal under the beak of the left valve which is often reflected 
upward, and a compressed, sometimes rudimentary tooth in 
front of it, the large tooth cutting off the hinge plate in the right 
valve; one cardinal in the right valve which falls between the 
two in the left valve; laterals blurred, generally having irregular 
ridges sloping back and downwardly on the hinge plate. 
Animal: Much as in Unio; inner gill either wholly free from 
the abdominal sac or more or less united to it. Outer gill of 
female filled entirely with embryos when gravid; anal opening 
smooth or only slightly cornulate. (Simpson. ) 
KEY TO SPECIES OF ALASMODONTA. 
A. Shell large. 
a. Shell compressed. 
ie) Eleight nearly equal toilength..02....5.002<: sa 0x complanata 
Peet hiatal lEWetie. < os. fe sisson c kesee oe 2 rugosa 
3. Similar to 2, but lateral teeth well developed 
qed aimbonal sculptire finer. 202... 05 0... let ed pressa 
b. Shell inflated. 
Pee bresdtmone-halfvol length! 25/5. \fas +. 6s,celats + sieida be marginata 
PyeSHel  sMmiallpaie UAC CALL es ccis hale Ac oclacs ooeciieesssacceaees deltotdea 
GROUP OF ALASMODONTA RUGOSA. 
4. Alasmodonta rugosa Barnes, pl, viii., figs. 3, 4, pl. vii., figs. 1, 2. 
Alasmodonta rugosa BARNES, Amer. Journ. Sci. and Arts, 1st series, Vol. 
VI., p. 278, pl. xiii., figs. 21a, 21b, 1828. 
Shell; Elliptical, rather thick, not inflated (the female is a 
trifle inflated), rounded before and obtusely angulated behind; 
dorsal margin straight, ventral margin straight in the male and 
curved in the female; umbonal slopes almost flat in the male 
and slightly rounded in the female; surface marked by heavy 
growth lines which form strong wrinkles on the dorsal part of 
the posterior angle; umbones neither elevated nor inflated, 
light brown in color, frequently eroded, and marked by three 
strong, almost straight, elevated ridges, the apex directed 
anteriorly; ligament long and narrow, dark horn color; epider- 
mis yellowish green, delicately rayed with dark green; cardinal 
teeth thick and heavy, more or less pyramidal, striated on the 
upper surfaces; lateral teeth rudimentary, being little more 
than a thickening of the hinge plate; anterior adductor muscle 
scar very wide, deeply impressed, slightly striate and irides- 
