266 PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 



lateral walls of the carapace. It is evident, from the study of these 

 transitious, that the form of the carapace caunot furnish a certain basis 

 for the establishment of distinct genera. 



"The character of the spines has, however, a greater value than tliat 

 of the form of the carapace. Although it be true that spines do not 

 occur exclusively upon this or that form of carapace, since there are 

 triangular Irunkflshes without spines, others armed with frontal and 

 anal spines, and others with anal spines alone, while there are also 

 quadrangular ones, spineless, or armed on the forehead and beneath the 

 tail, still there may be observed a certain consistency in their arrange- 

 ment as regards their position, their form, their number, and their di- 

 rection. But this constancy does not extend to their persistency since 

 some S])ines, or indeed all of them, are absorbed and disappear entirely 

 in adult individuals of certain species. In this manner all the spines 

 disappear with age in Ostracion concatenatus, and if one were disposed 

 to see generic characters in its arming, three genera might be founded 

 upon O.stracion stellifer, Bl., Schu. (in which the forehead, the dorsal 

 keel, and the ventral ridge are spinous), Ostracion hicuspis, Blum., figured 

 by A. Smith (which has only dorsal and ventral spines), and Ostracion 

 concatenatus, Bl. (which has the carapace entirely spineless). In real- 

 ity these species are merely nominal ; Ostracion stellatus and Ostracion 

 hiciisjns being young individuals of the species of which 0. concatenatus 

 is the adult. In one other species, Ostracion cornutus, Linn, (not Bloch), 

 the spines in the middle of the lateral dorsal ridge, and those on the 

 ventral ridge, decrease with age, and in the adult finally disappear. 

 In other species the spines are much more constant, but their i)ropor- 

 tions, very different in accordance with the age of the individual, render 

 it sufficiently evident that they afford a character of very doubtful 

 value. I should, however, note the fact that there is no known example 

 of an Ostracion with horizontal frontal and anal spines in w^hich these 

 spines disappear in adult age." 



As has already been stated, the subgenera adopted by Bleeker are 

 founded solely upon the number and position of the spines. In Tetro- 

 somus he ])laces one pentagonal species, but in Acantliostracion and 

 Ostracion he includes triagonal, tetragonal, and pentagonal forms with- 

 out discrimination. Notwithstanding the strong grounds taken by him 

 in regard to the importance of the shape of the carapace it seems to 

 afford the most reliable guide in an arrangement of the species of this 

 genus. An arrangement Avith reference to the position of the spines 

 produces some incongruous results, while the other plan harmonizes to 

 a great extent with all structural features as well as with the geograph- 

 ical distribution of the group. Hollard remarked that the serial grada- 

 tion of the species was of great interest, but he did not work it out 

 with the care which might have been expected. I have endeavored to 

 indicate what seems to me to be a natural series, from the triagonal 

 spineless form through the pentagonal form, provided with many spines, 

 to the tetragonal spineless form at the other extreme. 



