THE NATURAL HISTORY SURVEY. 65 
KEY TO THE SPECIES OF UNIO.* 
I. Shell generally thin, cardinal teeth but slightly developed, hinge 
line slightly thickened. 
a. Shell large, 45 mill. or more in length. 
1. Umbones large and coarsely wrinkled. 
7Ground color of shell yellowish horn with 
dark green rays sometimes uniform dark 
brownish or blackish; posterior end 
broadly rounded, almost truncated.......... edentulus 
+7Ground color of shell greenish straw or light 
green with light green rays; posterior end 
acutely rounded. Umbones not so coarsely 
SUSARCULSDESTURARL hyo Seas BY abdhin dicrauarnd oy ase i atta yx Sea IN pavonius 
2. Umbones small and finely wrinkled. . 
7Color light green or blackish horn, shell 
elliptical, posterior end broadly rounded 
J EADS CODER UGOS e SOD DR Chin. 15 oC OEE RENE Serussacianus 
7TColor yellowish horn, shell subcylindrical, 
posterior end acutely pointed........... subcylindraceus 
b. Shell small, long and narrow, 35 mill. in length....... hildrethianus 
II. Shell generally solid, cardinal teeth well developed and hinge 
line with well developed lateral teeth. 
A. Shell smooth, with distinct rays. 
1. Length 2% times height. 
a. Epidermis yellowish, plain or distinctly rayed with 
bright green, nacre white or pinkish................ anodontoides 
b. Epidermis very dark green or black, rays faint, nacre 
FIGHHPULMleL ae sete A ateere cdc ee marae Wlattere wy stacaria ait of oiaane ates rectus 
2. Length about twice height. 
a. Shell large, inflated laterally, cylindrical, rays very 
ABO aecahag 8.508 5 u(ceriiln sss bayrceeh ait aiaepeasaietsia upelatnipiare ks «s luteolus 
b. Shell smaller and more pointed posteriorly than a; rays 
wide; shell much compressed. 
+Rays interrupted forming square spots............ iris 
77Rays not interrupted, continuous; larger 
Bed Micke SAUGEHANGT iy csja debi n > Cnc ek een spatulatus 
3. Length one-third greater than height. 
a. Shell alate. 
*Shell rather thin, lateral and cardinal teeth 
thin and weak; color light yellowish with 
PETE OTC TAS), bie og Miehccin sjeialn y tivwlastacb\d sia welere gracilis 
+tShell solid, lateral and cardinal teeth solid; 
color dark green or black with fine rays......... alatus 
b. Shell not alate, rays in straight lines. 
tShell inflated. 
*Shell large, rays wide and few innumber.. . . ventricosus 
*For the purpose of simplifying the work of determining the species of Unio, Stroph- 
itus, Anodontoides, Quadrula, Obliquaria, Plagiola and Lampsilis, the author has made a 
single key to contain all the species of these genera, thus doing away with the confusion 
which would follow the splitting up and placing of the key among these newly-recognized 
groups. 
