SUPPLEMENT. 



Triplesia extans. 



^J^ 



S93 



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 Ambontchia and Paljsabca, 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 PALiEARCA 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. 



