MUSSELS OP CUMBERLAND RIVER AND TRIBUTARIES. 45 



DISCUSSION OF MUSSEL SPECIES. 



In the list of species here presented we have followed in most 

 respects the classification and sequence given in Simpson's well- 

 known Synopsis of the Naiades. In the spelling of the names, 

 however, we have followed the suggestions of Lindahl ® and have 

 made also a few minor changes, such as the substitution of the older 

 name Quadrula undata for Quadrula trigonaj as suggested by Mr. 

 Bryant Walker, and the transference of the Medionidus subtentus 

 (Say) to the genus Ptychohranchus, and of Tritogonia tuherculata 

 (Barnes) to Qvxidrula under the name Quadrula tritogonia^ as sug- 

 gested by Dr. Ortmann. Many other changes have been proposed 

 which will probably in the end prove justifiable. We have avoided 

 making any shifts between Pleurohema and Quadrula, although sev- 

 eral have been advocated which may be desirable. The fact that 

 both Pleurohema dssopus, Quadrula ohligua, and another perplexing 

 form which we have found may have glochidia in two, three, or all 

 four gills indicates that these two genera should reaUy be united. 



We are very favorably incUned toward the new classification pro- 

 posed by Ortmann,^ but its present state of incompleteness and the 

 uncertain position of many species, as well as our own conclusions 

 regarding Quadrula and Pleurohema, make it seem best at present 

 to use the older and better known system with the few exceptions 

 noted above. 



1. Truncilla triquetra Rafinesque. Snuffbox. 



This attractive little shell occurs only in the upper part of the river. In all we 

 procured 21 specimens, 19 of which were obtained at Salt Lick Bar. In the autumn 

 of 1910 Mr. Boepple found it at Indian Creek, Cloyds Landing, Albany Landing, 

 and in the Obey River at Celina, Tenn. 



It is in all probability considerably more common and widely distributed in the 

 river than our collections would indicate. But it does not seem to occur as far down 

 the river as Half Pone Bar or at Clarksville; if it did a few examples would certainly 

 have been taken among the great number of small mussels collected in that region 

 in June. 



Truncilla triquetra is a small species, dwelling in the shallower water. On account 

 of its small size it is rarely or never taken on the mussel dredge or rake, but must be 

 gathered by hand. It has a handsome, strong and thick shell, but is too small to have 

 any commercial value. All our examples are pretty well eroded at the umbones. 



2. Truncilla brevidens (Lea). 



This species was not found in the main river at all and only at three stations alto- 

 gether. It was most abundant in the Big South Fork opposite Parkers Lake Station. 

 Three examples were procured in the same fork 2 miles above Burnside and one in 

 Beaver Creek. It is too small to have any commercial value. 



All the specimens found were dead, but some had been recently killed by muskrats, 

 therefore nothing was learned concerning its habits. It appears to be a species 



a Lindahl, J.: Orthography of names of the Naiades, The Journal of the Cincinnati Society of Natural 

 History, vol. xx, no. 5, art. vni. 



6 A monograph of the Najades of Pennsylvania, reprinted from the Memoirs o: the Carnegie Museum, 

 vol 14, no. 6, Feb. 15, 1911. 



