68 ANNUAL REPORT OF 



sented, four of which are known by a solitary species each. Of 

 the remaining genera, Catopterus and Semionotus, the latter is 

 numerically the more important, and is also represented by a 

 larger number of species. 



It is often difficult to distinguish the species of Semionotus 

 from one another, except in the case of well preserved individuals, 

 but the genera can always be separated with ease. The serration 

 oi the posterior scale-borders in Catopterus, and delicately 

 fringed condition of the anterior ray of all the fins, are characters 

 by which any member of this genus can be recognized at a 

 glance. The fringed appearance of the fins just mentioned is 

 due to' the presence of numerous spine-like splints or raylets 

 known as fulcra, which are peculiar to ganoid fishes — or those 

 having rhomboidal, enameled scales. According to the familiar 

 dictum of Johannes Muller, "every fish with fulcra on the an- 

 terior edges of one or more of its fins is a ganoid." The group 

 of fishes embraced in this category was vastly more important 

 during remote geological periods than in later times, and at 

 the present day it is on the verge of extinction. In fact, not 

 more than seven genera of the modern fauna can be classed 

 as ganoids, according to the more precise definition of this series, 

 the most familiar of these being the sturgeon (Acipenser) , gar- 

 pike (Lepidosteus), and bow-fin (Ainia). Recent ganoids, with 

 the exception of the sturgeon, have acquired a fresh-water 

 habitat, whereas their predecessors were chiefly marine. 



It is probable that the Triassic fishes we are about to con- 

 sider belonged to a more or less brackish-water fauna, as there 

 is abundant evidence to show that the shallow-water sediments 

 of the Connecticut Valley Trias, and of the Newark series in 

 New Jersey, were deposited under estuarine, or off-shore condi- 

 tions. It need scarcely be remarked that of this exclusively ganoid 

 fauna, all the genera are now extinct. One of them, Dipluriis, 

 belongs to the Crossopterygian or fringe-finned ganoids, of which 

 there are but two living representatives — Polypterus and Cala- 

 moichthys. The remaining five belong to the group of Actinop- 

 terygian fishes, and one of the number, Catopterus, is interest- 

 ing in that it stands close to the ancestral line of the sturgeons, 

 which originated as far back as the Devonian. 



