110 Dr. C F. Liitken on the Changes of Form in Fishes 



unnoticed (see the fig. on p. 512 of tlie Danish memoir), 

 namely the existence or absence of teeth on the pterygoids 

 side by side with those of the palatines and vomer, in accor- 

 dance with the following scheme, the divisions of which must, 

 however, only be estimated as sections or subgenera, and not 

 as true genera : — 



A. 4-5 (6) dorsal spines ; scales linear ; no teeth on the 



pterygoids. C. occidentalis, salieJis, jpalomefa {Oligo- 

 plites, Gill). 



B. 7 dorsal spines, and teeth on the pterygoids. 



1. Scales linear: C. tol {C. moadetta, Klz., perhaps the 



young form of C. tol). 



2. Scales short and broad : C. Ii/son, sancti Petri ^ and a 



new species from Singapore which greatly resem- 

 bles C. alius of the western coast of Central 

 America. 

 In some species the teeth of the upper jaw are uniserial, 

 and in others bi- or pluriserial ; but those of the mandible are 

 always biserial, although here a remarkable difference due to 

 age makes its appearance ; the older individuals are homodont^ 

 and the young heterodont. In other words, in the young 

 Chorinemi, until they are about half-grown, the outer row in 

 the mandible consists of very small, numerous, setiform teeth 

 placed very close together (almost as in the Chsetodonts), 

 wliich are very different from the strong, conical, recurved 

 teeth, separated by distinct intervals, and consequently much 

 less numerous, of the inner row. During the growth of the 

 fish these outer teeth are replaced by a new row of teeth, 

 which, according to the species, are identical with, or more or 

 less similar to those of the inner row. A somewhat super- 

 ficial observation of these important modifications of the 

 dental system, which depend u]Don the age of the individual, 

 might easily lead to the establishment of unfounded specific 

 distinctions. The pterygoidian teeth, mentioned above, 

 likewise exist in the genus Paropsis ; and this genus presents 

 another peculiarity not previously mentioned, namely the 

 ramification of the lateral line, which, however, seems to be- 

 come less marked with increasing age. 



10. PsENES, CuBiCEPS, and Navaechus. 



It is already known that Navarchus is generically identical 

 with Atimostoma and Trachelocirrus, as also that this genus 

 falls into that of Cubiceps. But in the present state of science 

 it is equally difficult to separate the genera Psenes and Cubi- 

 ceps. Under these two names a series of species have been 

 described which are for the most part young forms still un- 



