147] FAUNA OF BIG VERMILION RIVER—BAKER 49 
milion specimens. A long narrow pearly blister on the posterior margin of 
one specimen might have been due to the presence of the marginal distomid 
described by Kelly. Clark and Wilson (1912:62) found this distomid com- 
mon as cysts in ligamentina from the Maumee River. A specimen from 
the Big Vermilion had a large pearl-like blister at the lower edge of the 
posterior adductor muscle scar. (Z 11482 A). An abnormal shell without 
the animal, was found in Middle Fork. The posterior end is sharply trun- 
cated and bent inward in the right valve and bent outward in the left valve. 
The hinge teeth are much more elevated and heavier than in normal speci- 
mens. This abnormality was due to an injury received when the shell was 
about three years old. It must have lived upward of two years after 
receiving the injury, judging by the rest marks on the shell. This individual 
measures length, 84, height, 52 mm. (Z11216A). 
The Middle Fork and Big Vermilion shells are thick and of good, clear, 
pearly-white lustre. The mucket is one of the most valuable shells for the 
cutting of button blanks and the Middle Fork and Big Vermilion speci- 
mens appear to be of excellent quality for this purpose. The species from 
this stream could be used for glochidial infection of fish. Gravid females 
were collected on September 26. Ligamentina was not found in the Sanga- 
mon River.- 
27. Actinonaias ellipsiformis (Conrad). 
This small naiad occurs rarely at three places in the Big Vermilion 
River; below the dam at Homer Park, in the Salt Fork south of Muncie, 
and in the Big Vermilion below Middle Fork. Whether this rarity is due 
to a real scarcity of the mussel or to the inability of the collectors to find it, 
is not known. Diligent search was made in the various places visited, 
and the fact that but few specimens have been found by Professor Smith 
after years of constant collecting at Homer Park, leads to the conclusion 
that the species is rare in this stream. 
Ellipsiformis is common in the Sangamon River at Mahomet where it 
occurs on a sand and gravel bottom, more commonly on riffles, where the 
current is rather swift. The shells from this station are not large (maximum 
size, length, 63, height, 31 mm.) but are very thick, with pearly-white 
nacre. The shape is normal, the posterior end being sharply pointed with a 
narrow truncation. The color is yellowish or greenish with many dark 
green rays, often wavy. Rest periods show as elevated longitudinal ridges, 
especially near the ventral margin of the shell. A half-grown specimen, 
length 38, height 23mm., resembles in outline young shells of Actinonaias 
ligamentina and if found with that species would probably be so identified. 
Ligamentina, however, is not found at Mahomet, and this specimen is 
doubtless referable to ellipsiformis. Utterbach’s reference of the species 
to the genus Nephronaias (= Actinonaias) is strengthened by the similarity 
of these shell characters, which this author has also noted (1916: 142). 
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