141] FAUNA OF BIG VERMILION RIVER—BAKER 43 
continued its shell formation so perfectly that from the outside no evidence 
of an injury is visible. This shell indicates plainly a case of a hard struggle 
for existence against both mechanical injury and heavy parasitism. The 
interior of the shell is spotted with grayish patches and salmon-colored 
streaks (No. Z11029-A). (Figs. 22,23.) 
14a. Anodonta grandis gigantea Lea. Floater. 
Specimens of an Anodonta from Crystal Lake, Urbana, are apparently 
referable to Lea’s gigantea. Simpson (1914:420) diagnoses this variety 
as ‘Shell large, ovate or subrhomboid, a little higher in proportion to the 
length than the type; beaks full and high.” The specimens from Crystal 
Lake agree with this diagnosis. The largest individual measures 152 mm. 
in length and 92 mm. in height. The umbonal region is more corpulent 
than in the grandis from the other parts of the Salt Fork. The color 
is brownish or greenish, the two colors frequently in alternating zones 
on the same specimen. Evidences of distomid infection are common in the 
form of salmon or pink discolorations and ridges. One individual has many 
long, thin, curved ridges on the interior of the shell, principally in the left 
valve. One of these ridges measures 93 mm. in length and 1.50 mm. in 
height (Fig. 24). Another individual has a round pearl attached to 
the posterior end of the shell, measuring 5 mm. in diameter. This variety 
has not been observed in any collections from the Big Vermilion or Sanga- 
mon rivers. Marsh has recorded gigantea from the Big Vermilion (Baker, 
1906:73) but the exact location is not known, and must have been below 
the points examined by the writer. 
15. Anodonta corpulenta Cooper. Floater. 
The large Anodontas from Crystal Lake are divisible into two groups; 
one is the variety of grandis described above; the other seems to be the 
corpulenta of Cooper, although the shells are smaller than examples of 
this species from other rivers. The shells referred to corpulenta are sub- 
rhomboid, somewhat elongated in a few of the individuals. The umbonal 
swelling is very pronounced, extending well downward on the shell. The 
anterior end is broadly rounded and the posterior end is distinctly plow- 
shaped and rather strongly biangulate. The epidermis is olive or brownish. 
The surface is very rough, the growth lines in some specimens being 
elevated into longitudinal ridges. As in gigantea, the inner surface is 
ridged and salmon-colored in many specimens due to the presence of 
distomid worms. No specimens of this species were seen which did not in 
some degree show evidences of the work of this parasite. Characteristic 
measurements of this shell are given below (Z11368): 
Length, 127; height, 82; breadth, 53 mm. 
see 49 sar riil «38 mm. 
[<3 128 “ 70 “e 50 mm. 
bl S64 “50 mm, 
