NO. 2.] SNAILS OF THE GENUS 10— ADAMS. 19 



have an adequate explanation for the scarcity of the shells. Unionidae were present, however, 

 as shown by the bivalves on the banks where they had been opened by raccoons or muskrats. 



Supl.lotl91. Mendota, Washington County, Va. October 13, 1900. Northwest of Bristol. 

 Bristol sheet. This locaUty is downstream from Holston about 17 miles and 42 from Saltville. 

 This is the county from which the type of spinosa Lea is said to have come, but evidently this 

 is an error. 



About a half dozen shoals were examined while ascending the river for 3 or 4 miles. The 

 conditions seemed favorable, but no live lo were found, although three dead and worn shells 

 were obtained; one was a smooth shell, the others are undulated. These shells are apparently 

 nearer the Saltville shells than to verrucosa. 



Supl. lot 116. Holston Bridge, Va., 2J miles east of Big Moccasin Gap, Va. August, 1901. 

 Estillville sheet. This series consisted of 3 live specimens and 19 dead shells. The individuals 

 are all rather nodulose and similar to those found at Bluff City on the South Fork, lot 94. 

 They are thus strictly transitional between fluvialis from Saltville, lot 79, and the spinose 

 shells farther downstream. 



Supl. lot 111. Holston Bridge, Va., 2^ miles east of Big Moccasin Gap, Va. August 11, 1901. 

 Ten fresh shells. Estillville sheet. This is about 25 miles downstream from Mendota. There 

 is a marked change in the character of the lo shells; they approach those of the South Fork 

 (verrucosa) rather than those of Saltville. It is unfortunate that the details of the transition 

 in the North Fork are so little known. A reexamination of the river should be made upstream 

 from this point. Compare with lot 178, from near the mouth of the North Fork. 



Another feature of interest is the proximity of this portion of the river to Big Moccasin 

 Gap, plate 59, and hence its bearing upon changes in drainage. 



About 15 miles below this locality the North and South Forks of the Holston are confluent 

 at Rotherwood, Tenn., and form the Holston trunk stream. It is about 80 miles from Saltville 

 to Rotherwood. 



b. Middle and South Forks of the Holston. 



The conditions for examination of the Middle Fork of the Holston were unfavorable on 

 account of the recent rains and the vast quantities of yellow clay which discolored the water. 

 A search was made, however, at Seven Mile Ford, also south of Glade Springs, Va. The South 

 Fork apparently does not drain as much of a limestone area as the Middle Fork, because its 

 waters were clearer. At Holston Mill and near Friendship, Va., the waters were clear, the 

 shoals apparently favorable, but no lo were found. The probabilities are that lo does not occur 

 in the Middle Fork, nor in the South Fork, above the junctions of the two streams near Barron, 

 Va. I examined the streams at this place (and the South Fork upstream as far as Damascus, 

 Va.) with considerable care, but found no evidence of them upon the rocky shoals which abound 

 in the Middle Fork near its mouth or on the sandbar below the junction where the railroad 

 crosses the South Fork. Cf . Abingdon sheet. 



Group 13. Supl. lot 115. Fishdam, Tenn. This locality is downstream from the con- 

 fluence of the Middle Fork of the Holston about 15 miles. It may be reached from Bristol, 

 Tenn., by a narrow-gauge lumber railroad, the Holston Valley Railroad. At Fishdam there 

 is a large shoal with many bowlders. The river was a little high, so that only dead shells of 

 verrucosa were found here August 31, 1901. This lot gives the known upstream limit in the 

 South Fork of the Holston. Abingdon sheet. 



Supl. lot 120. Fishdam, Tenn. One hve lo verrucosa was found here September 7, 1901. 

 A number of dead shells were also found, thus establishing the type for the locality. The water 

 was very clear and the bottom could be clearly seen in water knee-deep. Shoals, islands, and 

 sluices were examined for about 3 miles upstream. Several apparently very favorable places 

 were seen, but the only results were those stated above. 



Supl. lot 157. Fishdam, Tenn. While in this series perfect and fresh shells are too limited 

 for detailed statistical study, yet this large series gives a good sample of the verrucosa popula- 

 tion. CoUected by John A. Ofiield, October, 1901. A few sheUs (10) were in excellent and 

 fresh condition. 



