98 
Aug. F. Foerste 
According to the preceding observations, Rhyuchonella whitii^ 
Rh. neglecta, and Rh. indianensis are congeneric. This group is 
believed *to include also Rhyuchonella bidens, and Rhyuchonella 
acinus. That these shells do not belong to Camarotoechia is shown 
by the thin, lamellar cardinal process. That they do not belong to 
Rhynchotrema is shown by the much smaller, oval muscular area, 
quite different in form and in the general arrangement of the mus- 
cular markings. The nearest relative undoubtedly is Rhyncho- 
treta cuneata, to which genus it may belong. To determine this, 
the delthyrium must be studied. This delthyrium is not preserved 
in the specimens at hand in such a form that any opinion can be 
expressed with confidence. The general form of Rhynchotreta is 
very different, but this may be a specific, rather than a generic 
characteristic. To distinguish the species typified by Rhyncho- 
treta whitii-proe cursor^ from the more typical species of Rhyncho- 
treta, possessing an acuminate beak, long broad flattened sides, 
and a median depression along the posterior parts of the brachial 
valve, the term Stegerhynchus may be employed. 
Camarotoechia lindenensis. 
{Plate 7, Fig. Jj.) 
The generic affinities of this shell can not be determined defi- 
nitely since the interior is unknown and the tip of the beak is poorly 
preserved; however, as far as can be determined the beak of the 
pedicel valve was not perforated. Outline approximately circular; 
length, 19 mm.; width, 23 mm.; thickness, about 11.5 mm. The 
specimen may have been thicker originally, but it evidently con- | 
sisted of a shell of only moderate convexity. Median fold and | 
sinus distinct, rather narrow and of only moderate elevation and I 
depth, the fold rising only 2.5 mm. above the adjacent part of the i 
shell at the anterior margin. Three radiating plications on the I 
median fold, two in the sinus, 8 or 9 on each side. Plications 
rather sharply angular along the top, crossed by fine close striae i 
distinctly visible under a lens. ! 
Brownsport bed: near E. Duncan, one and one-half miles east 
of Linden, Tennessee. 
