SUPPLEMENT. 
32 3 
Triplesia extans. 
12 3 
Fig. 1. Ventral valve. Fig. 2. Dorsal valve. Fig. 3. Area and foramen of the 
ventral valve. 
SUPPLEMENTARY NOTE ON THE GENUS AMBONYCHIA. 
[ For Observations on the Genera Ambonychia and Pai.^earca, see pp. 269 - 272 of this volume.] 
Since the preceding pages were printed, I have been able, through the 
kindness of Professor Safford of Tennessee, to illustrate more fully the 
hinge-structure of Ambonychia radiata. The accompanying figure 1 shows 
the hinge-line, the cardinal teeth t, and the lateral teeth tt. On the ante¬ 
rior side, the margin of the shell is sinuate for the passage of the byssus 
b. The latter character is likewise more distinctly shown in figure 2, which 
is an anterior view of the right valve, 
At the time that my examinations and descriptions of Paltearca were 
made (in 1857), I had overlooked the Genus Cypricardites of Conrad, which 
was published in the Annual Geological Report for 1841. The description 
and figure correspond so nearly with the fossils which I have described, 
