FRESH-WATER MUSSELS. 

 Table 21. — Maximum Size of Young Lake Pepin Muckets at Various Ages. 



159 



Age. 



Beginning of juvenile stage 



IS days 



38 days 



Length. 



Millimeters. 

 o- 25 

 ■5 

 4.3 



Inches. 



Age. 



6Sdays 



5 months 



End of second growing 



Length. 



Millimeters. 

 13- o 

 32-3 

 5«-3 



Inches. 



0.51 

 1.27 

 2.30 



This species displays perhaps the most rapid growth of any commercial mussel, 

 although it is surpassed in this respect by some of the noncommercial floaters and 

 paper-shells. The maximum size attained in the second year by mussels ot several 

 other species reared at the Fairport station is given in Table 22. 



Table 22. — Size and Age of Mussels Reared at Fairvort Station. 



Spedes. 



Remarks. 



Lampsilis ligamerttina, mucket 



Lampsilis anodontoides. yellow sand-shell . . 

 Obliquaria reflexa, three-homed warty-back 



Plagiola donacilormis 



Quadrula plicata, blue-point 



Quadnila undata, pig-toe. 



Obovaria ellipsis, hidcory-nut 



Accidentally reared. 

 Intentionally reared. 

 Accidentally reared. 



Do. 



Da 



Do. 



Do. 



Much remains to be learned regarding the habits and habitats of the juvenile mus- 

 sels of many species. The study is somewhat difficult, because mussels in the juvenile 

 stage are usually hard to find. This is the experience of all collectors, although rich 

 finds of larval mussels are occasionally made in particular locations (Howard, 1914, 

 pp. 34 and 47). In 1914 Shira collected 1,394 juveniles representing 16 species in Lake 

 Pepin, and 92.9 per cent were taken upon sand bottom where there was scattering vege- 

 tation. This figure can not, however, be taken as an index of preference for that par- 

 ticular sort of habitat, since 86.2 per cent were taken at one station. Isely (191 1, p. 78) 

 made a collection of 32 juveniles comprising 9 species, 6 of which were represented in 

 the Lake Pepin collections, but Isely's specimens were all taken in fairly swift water, 

 I to 2 feet deep, and from a bottom of coarse gravel. In rearing young mussels, prin- 

 cipally Lake Pepin muckets, in ponds at Fairport, the best success has been attained 

 on prepared bottom of sand; yet when Howard reared Lake Pepin muckets in a crate 

 floating in the river, silt accumulated to a considerable depth, and the juvenile mussels 

 were sometimes found deeply submerged in the soft mud; nevertheless, more than 200 

 young mussels survived the season in a very small crate, and excellent growth was made. 



After the byssus is shed the young mussels often bury themselves in the bottom 

 more deeply than do adults. They are inclined to travel considerably at this stage, 

 but the rate of movement and the distances covered are less than might be thought 

 from observation of the conspicuous and apparently fresh tracks behind the young mus- 

 sels. It has been found that the tracks will retain the appearance of freshness for sev- 

 eral days; hence the trail which one might at first suppose to have been made in a few 

 hours may represent a journey covering a considerable period of time. Clark observed 

 a young mussel which made forward movement every 10 seconds, each movement being 



