1895.] On the Validity of the Genus Margaritana. 341 
found from a narrow to a heavy hinge plate, and the same is 
true among the Unios I have just mentioned.’ 
Margaritana holstonia and. M. georgiana, the latter being per- 
haps synonymous with the former, so closely resemble some 
of the Unios of the group typified by U. nashvillensis that Dr. 
Lea himself sometimes referred specimens of them to some of 
these species, and their only essential difference is that they 
are generally destitute of the lateral teeth which are present in 
the Unios. 
Such species as Margaritanar liana, spillmanii and related 
forms have no laterals, and only partially developed cardinals. 
In most of the specimens the hinge line is incurved in the 
region of the rudimentary cardinal teeth, exactly as in the so- 
called Anodonta edentula and its allies, all of which bear close 
relationship to them, and I believe that they should all be 
placed in the genus Unio, since their animals, so far as is 
known, agree well with those of that genus. 
1! Lea’s description of the soft parts of Margaritana confragosa agrees very 
closely with that of Unio lachrymosus, which is synonymous with U. asperrimus 
Unio lachrymosus Lea. | Margaritana confragosa Say. 
Branchiæ very large, inner ones | Branchix very large, nearly semi- 
very much the larger, rather thick, circular, inner ones much the larger, 
very much rounded below, free nearly | free the whole length of the abdominal 
an whole length of the abdominal | sac 
me | 
T Pipi very large, transverse, rather Palpi very large, pendant, mney 
thin, subelliptical, united half way | united half way down the poste 
down the posterior ed edges 
Mantle rather thin, with a broad | Mantle rather thin, with a thickened 
thickened margin. broad margin 
Branchial opening very large, with Branchial opening rather large, with 
numerous rather small, branched | numerous small, brown papillz. 
papille. 
Anal opening rather small, without Anal oa very small, with very 
papille. minute papill 
Super-anal opening very large, Gupeanat be opening large and united 
slightly colored on the edges, united | below, with a dark line on the inner 
for asmall distance below, color of the | edges. Color of the mass whitish. 
mass whitish. 
The above are Lea’s descriptions of the two species. 
