788 THE AMERICAN NATURALIST. (VoL. XXXIII. 
in all recent works has been known as M. hibberti becomes 
Parabatrachus maxillaris Agassiz. Other British species. are 
P. coccolepis (Young), P. intermedius (Woodward), P. laticeps 
(Traq.), P. pygmaeus (Traq.), and P. lævis (Traq.). The Amer- 
ican species are P. nitidus (Cope), P. cicerontus (Cope), and P. 
macropomus (Cope). P. maxillaris possibly also occurs in this 
country. P. nitens (A. Fritsch) occurs in Bohemia. 
Certain well-known genera and one species of pycnodont 
fishes bear names that are not tenable. 
In 18721 Dr. Leidy described a pycnodont, which he named 
Pycnodus faba. But already in 1847? H. von Meyer had given 
the same name to remains from the Eocene of Germany. 
Leidy’s species may then be given the name P. phaseolus, in 
allusion to the resemblance of the larger teeth to the pods of 
the wild bean, Phaseolus. 
As Mr. A. S. Woodward tells us,® the generic name Microdon, 
which has been used so long for a genus of pycnodonts, being 
proposed by Agassiz in 1833,* had been used previously in ento- 
mology by Meigen in 1803. It is, I am informed, now in cur- 
rent use as a genus of Diptera. If this name may be employed 
in both ichthyology and in entomology, its seems reasonable 
that the conchologists may be allowed to resurrect Conrad’s 
Microdon ; and we might then discuss the question whether the 
fish Microdon subsisted wholly on such mollusks as Microdon, 
or occasionally varied its diet by adding such Diptera as 
Microdon. I regard it as subversive of the purposes of 
scientific nomenclature to perpetuate the use of such preoccu- 
pied names. As I find no synonym of Agassiz’s Microdon 
which may take its place, it becomes necessary to propose 
a new name. This is PoLypsepuis, from qroAuwndis, with 
many pebbles, in allusion to the numerous rounded teeth. No 
American species are at present referred to this genus. 
Mesodon of Wagner (1851)° is not available in ichthyology, 
1 Proc. Acad. Nat. Sci. Phila., p. 163. 
2 Neues Jahrb. Min., p. 186. 
8 Cat. Foss. Fishes, vol. iii, p. 221. 
* Poissons Foss., vol. ii, pt. i 
5 Abhandl. k. bay. Akad. Wiss, antic phys. Cl., vol. vi, p. 56. 
