734 
BULLETIN OF THE BUREAU OF FISHERIES 
BUCKHORN AND POPE’S PURPLE 
ToJ|test the applicability of the ring method to studies of growth in species 
belonging to other genera, 16 specimens of the buckhorn, Tritogonia verrucosa (Eafin- 
esque), Tritogonia tuberculata of authors, from the Mississippi River at Fairport, 
Iowa, and 7 specimens of Pope’s purple, Unio popei Lea, from the lower Rio Grande 
Valley in Texas, were weighed and measured. 
The buckhorn is a heavy, comparatively slow-growing shell, ranging (Simpson, 
1914) throughout the Mississippi drainage system generally, and streams tributary 
to the Gulf from Alabama to central Texas. This shell has some commercial value. 
Pope’s purple is a moderately thin, rapidly growing shell, ranging (Simpson, 
CMS. 
GMS 
60 
50 
40 
30 
20 
I 0 
0 
Figure 19. — Median curve, together with first and ninth deoil curves of growth in length for the buckhorn from 
Fairport, Iowa. Maximum and minimum cases for various year classes are represented by the locality 
symbol transfixed by a horizontal line. Also curve showing mean weight on age for the eighth, ninth, and 
eleventh year classes 
1914) through southern Texas and northeastern Mexico. This species, although 
purple in color, has considerable commercial importance, as the shells can be bleached 
quite readily to a good, usable white color. 
Table 13.- — Length in relation to age of male and female buckhorns, 'Tritogonia verrucosa (Rafinesque) , 
Mississippi River, Ioiva 
[All values in centimeters] 
Ring No. 
Number of 
specimens 
Minimum 
First decil 
Median 
Ninth decil 
Maximum 
I 
16 
1.0 
1.23 
1.49 
1.88 
2.0 
II 
16 
2.2 
2. 32 
3. 35 
3. 77 
3.8 
III 
16 
3.2 
3. 48 
4.35 
4. 94 
5.0 
IV 
16 
4.2 
4. 48 
5. 36 
6.24 
6.4 
V 
16 
4.8 
5. 46 
6. 00 
7. 08 
7.2 
VI.. 
16 
5.4 
5. 92 
6. 56 
7. 68 
7.8 
VII 
16 
6.6 
6. 76 
7. 30 
8.88 
9.0 
VIII 
16 
7.0 
7. 60 
7. 80 
9. 68 
9.8 
IX 
2 
8.69 
9. 59 
10.49 
X .... . 
1 
11.01 
XI 
1 
11. 39 
