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BULLETIN OF THE BUREAU OF FISHERIES 
of the shell in front of the posterior ridge and by the more or less inflated character 
of the posterior outline of the shell, the females and males have been considered separ- 
ately. Owing to the small number of specimens of Unio popei Lea and Tritogonia 
verrucosa (Rafinesque) used, no separation of the sexes was made in these species. 
MATERIAL 
In the present studies two species — the yellow sand shell, Lampsilis anodontoides 
(Lea), and the Lake Pepin mucket, Lampsilis siliquoidea pepinensis Baker ( Lampsilis 
luteola of authors) — have been given particular consideration because of their com- 
mercial importance. In addition, the buekhorn, Tritogonia verrucosa (Rafinesque) 
or Tritogonia tuberculata, of authors, and Pope’s purple, Unio popei Lea, were used 
for certain comparisons. In all, 1,107 specimens were examined. Of these, 600 
were Lake Pepin muckets, 484 yellow sand shells, 16 buckhorns, and 7 Pope’s purple. 
INDIVIDUAL SPECIES 
YELLOW SAND SHELL 
The yellow sand shell, Lampsilis anodontoides (Lea), perhaps the most valuable 
single species of fresh-water mussel in North American waters, is found throughout 
the Mississippi River drainage system, with the possible exception of the upper 
Missouri. Simpson (1914) also records the species as occurring in the entire Gulfwise 
drainage area from Withlacoochee River, Fla., to the Rio Grande, and south into old 
Mexico. It is usually found on sandy bottoms in the larger rivers of its range but 
may also occur in the quieter portions of these streams on mud bottoms. 
In the present studies, shells from three localities — the Mississippi River, at 
Fairport, Iowa; the White River, at Newport, Ark.; and the lower Rio Grande, near 
Mercedes, Tex. — representing the northern, middle, and southern portions of the 
range of this species, have been examined. In all three localities the shells are 
commonly taken in sufficient quantities for commercial use. 
Fertilization of the eggs in the northern waters takes place during the later half 
of summer. The glochidia are developed by fall and are held in the marsupia until 
the following spring or early summer. Breeding seasons occasionally overlap. 
(See Lefevre and Curtis, 1912; and Coker, Shira, Clark, and Howard, 1921.) The 
ripe glochidia are extruded, and their parasitic stage begins some time in May or 
June. As their parasitic stage is usually completed in three weeks or less in northern 
waters, the free existence of the juvenile mussel probably begins about the first of 
July. This cycle gives a period of three or four months before the onset of cold 
weather and the formation of the first large interruption or growth ring. This period 
of growth for the first season is probably of 5 months’ duration in Arkansas and possibly 
7)2 months in southern Texas. The respective durations of the growing season after 
the first year are estimated at 5 months in Iowa, 7 in Arkansas, and 9 in southern Texas. 
The shells from the Mississippi River, at Fairport, Iowa, represented two 
independent collections. The first of these consisted of 100 valves from female 
mussels and 100 from males, as obtained from local shellers in the summer of 1926. 
These valves were not paired. This collection was used for growth in length deter- 
minations. The second Mississippi collection was obtained by local shellers in 1927, 
1928, and 1929 and consisted of 50 left valves from female mussels and 50 from males. 
These shells were used for growth in weight determinations. 
