IQ Genus Anomalodonta. 



ieties, for there are at Richmoiit], Indiana, two types of casts, and many 

 variations from these types ; and there are about Cincinnati casts that 

 vary in form and size from those that can be clearly identified with the 

 known species. And the saniG may be said of other localities within 

 the Cincinnati Group. A good shell, showing the exterior, may be 

 found, if looked for, that will send a flood of light over many of these 

 unsatisfactory and undistinguished casts. Indeed, it is likely that 

 there is not, to-day, a single fossil genus, in the Cincinnati Group, but 

 that will have new species placed under it by future discoveries, not- 

 withstanding that the hills of Cincinnati have been hunted by collec- 

 tors for more than forty years, and the prevailing impression that there 

 is nothing new under the sun. 



Genus Anomalodonta. — (S. A. Miller.) 



Character : Equivalve, inequilateral, byssal sinus on the anterior 

 side, immediately below the beak, cardinal tooth or elevation beneath 

 the umbone sloping posteriorly from the beak. Cartilage grooves 

 running from the cardinal tooth beneath the beak to the termination 

 of the vving posteriorly, and varying in number in the same species 

 with the size and age of the shell, and having the same number of car- 

 tilage grooves on the anterior side of the cardinal tooth, that run 

 together as they pass into the byssal sinus, immediately beneath the 

 beak, which vary in number under the same circumstances. Adduc- 

 tor muscular impression on the anterior side, below the byssal sinus. 

 The other muscular impression probably placed posteriorly on the 

 wing. 



This genus will include the Ambonychia alata (Meek). " Ohio Pal.," 

 vol. i, p. 131. Mr. James has a specimen of this species, which shows 

 enough of the hinge line to leave no doubt that it is not an Ambonychia, 

 and that it must be placed in this genus. And it will probably in- 

 clude the Megaptera easel (Meek and Worthen). "111. Geo. Sur."vol. iii., 

 p. 337, and "Ohio Pal.," vol. i., p. 132, because the general appearance, 

 and the apparent thickening of the shell on the posterior wing, renders it 

 most likely that it does not possess the internal markings of the genus 

 Ambonychia, and quite probable that it does possess the hinge line of 

 this genus. 



The Anomalodonta alata and Megaptera Casci are both found in the 

 upper part of the Cincinnati Group, in strata about the equivalent of 

 the Versailles rocks, where the Anomalodonta gigantea is found. The 

 Merjapiera Casei being found at Richmond, Indiana, and the Anomalo- 

 donta alata in the vicinity of Morrow, Ohio. 



