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, Si mm. 

 " 119 " 71 " 58 mm. 



" 128 " 70 *' 50 mm. 



" HI " 64 " 50 mm. 



