48 ME. W. S. ROWNTEEE ON THE 



The Cliaracmida3 constitute a well defined yet widely diversified family of Teleostean 

 fishes, falling under the division Physostomi. They are entirely restricted to the fresh 

 Avaters of Tropical Africa and America, a distribution in itself sutficiently curious. The 

 greater number of tlie five hundred odd species known are denizens of the Neotropical 

 region. No genus is rejDresented on both sides of the Atlantic. 



Amongst the more obvious and generally recognized characteristic features of the 

 family are : — 



The fusion and modification of the first four vertebrae, in relation to the Weberian 

 mechanism ; a physostomous air-bladder, transversely constricted, as in the Carps, into 

 an anterior and a posterior chamber ; usually an adipose second dorsal fin ; a non- 

 protrusible mouth, the upper margin of which is commonly formed by both premaxilla 

 and maxilla ; usually teeth on the jiremaxilla and the dentary, sometimes also on the 

 maxilla and the palatine ; pelvic fins abdominal ; pectoral fins set low on tlie body and 

 folding like the pelvic fins ; body covered with scales, cycloid or ctenoid ; head without 

 scales ; parietals separated by a longitudinal fissure, or united by a sagittal suture ; 

 opercular bones complete ; symplectic present ; a supraoccipital spine, often long ; 

 suborbitals usually large ; pyloric appendages present ; barbels absent. 



By the earlier writers on the subject the majority of the then known forms comprised 

 in this family were classed as Salraonoids, others as Clupeids. Johannes Miiller * 

 (1843-4) was the first to separate these and to include them in the Characinidfe, basing 

 this change on the possession by these forms of the Weberian apparatus. It was, 

 however, reserved for Sagemehl t (ISSlj to attach full weight to this character and to 

 unite together the families possessing it — the Cyprinidse, Siluridge, Characinidae, and 

 Gymnotidae — into one group, the " Ostariophyses." 



The general efi'ect of Sagemchl's paper is the establishment of three main pro- 

 positions : — 



(1) That the parts of the Weberian mechanism in the families named are homologous, 



implying community of origin, not simplv analogous, as previously held. This 

 conclusion he supports by arguments deduced from comparison of the shoulder- 

 girdle, the interparietal fissure and other cranial characters, the opercvilar 

 apparatus, and other structures. 



(2) That the Characinida^ fall naturally into three distinct subfamilies, no one of which 



can be regarded as being derived from another, but which have all branched off 

 from a common ancestral line. These he designates the Erythrinoids, the 

 Herbivorous True Characinidae, and the Carnivorous True Characinidaj. 



(3) That the Characinidse, and more especially the Erythrinoids, in numerous cranial 



and other features, recall the conditions fou.nd in Amia calva and, in a less 

 degree, in other Ganoids. 



* Joh. Miiller, " Ubcr deii Bau und die Grenzen der Ganoiden," Abhandl. der Berl. Akad. d. Wisscnsch., 1844. 

 t M. Sagemehl, " Das Cranium der Characiuiden," ilorpli. Jahrb., lid. x. 1SS4. 



