24 BULLETIN OF THE BUREAU OF FISHERIES. 
The shells are of about the same size as the niggerhead. Those 2.5 to 3 inches long 
are fairly large. Mr. Boepple reported that the Scioto and Duck Rivers yielded examples 
of maple-leaf 4 to 5 inches long. The maple-leaf mussels probably spawn in early summer 
and midsummer. 
Quadrula fragosa (Conrad) (Pl. VII) is a very rare species of the maple-leaf, more 
quadrate in form than Quadrula lachrymosa; while Tritogonia nobilis (Conrad), having 
a similar external appearance, is confused with the maple-leaf. 
The monkey-face, Quadrula metanevra (Rafinesque) (PI. VII), is found in relatively 
small numbers. It occurs infrequently in the large mussel beds, but is usually found 
near the bank or outside the main beds. Owing to the large pustules and the very 
uneven outer surface it is difficult to cut, but with careful handling it may be cut 
into a few blanks of small size which are of excellent quality. The shell is often used 
to advantage for cutting one 24 or 30 line button from each shell. In value the shell 
is sometimes classed with pig-toes. "The spawning time is early or midsummer. 
The rabbit’s foot, Quadrula cylindrica (Say) (Pl. VII), is a very long and narrow 
form that is familiar to the fishermen of the southern portion of the Mississippi Basin. 
It is too narrow, convex, and uneven of surface to be of value for button manufacture. 
One or the other of the purple pimple-backs, Quadrula granifera (Lea) (Pl. VI) and 
Quadrula tuberculata (Rafinesque) (PI. VI), is found in most large rivers of the 
Mississippi and Great Lakes Basins, but they are not generally distinguished. The 
species tuberculata is flattish and is probably found more often in the smaller or tribu- 
tary streams. Both species are found in small numbers scattered among others. 
Owing to the purple color of the nacre, the shells have no commercial value. The 
layers are said to split apart in cutting. The shells have a very attractive appear- 
ance and will take a beautiful polish when finished as souvenirs. ‘The mussels are of 
value in the rivers, since they produce a relatively high number of pearls. Scarcely a 
tuberculata could be taken in the Grand River in Michigan in 1909 without finding some 
sort of pearl formation. The spawning period is early summer. 
The three-horned warty-back, Obliquaria reflexa (Rafinesque) (PI. VI), is not at all 
closely related to the pimple-backs or purple warty-backs. It has one row of large 
knobs on each shell, and the knobs are remarkable in that those of the two sides 
are not opposite, but alternate in position; the species can not, therefore, be mistaken 
for any other. 
The three-horned warty-back is found in small quantities along with other mussels. 
The forward portion of the shell is thick, the tip thin. The form and the knobs are 
objectionable, and the size is not large, but the texture is good, and the nacre is clear 
and white and makes first-grade button material. 
The species is widely distributed in the Mississippi drainage and elsewhere. It 
appears to be a summer breeder. 
PIG-TOE GROUP. 
This group is rather limited both in variety of species and, except in certain streams, 
in general abundance of the mussels: None of the mussels is of the best quality. 
The pig-toe, Quadrula undata (Barnes) (Pl. VIII), is found in small quantities, prin- 
cipally in the Mississippi, and also in some of its tributaries. White River, Ind., has 
examples of unusually large sizes. While the material is somewhat similar to that 
