REPORT ON ICHTHYOLOGY. 413 



liiriis given by Rafiuesque is, perhaps, the best description of a genus given in his 

 work, and is thought worthy of being copied: 



"Head depressed, with eight barbs, one at each corner of tlie mouth, longer than 

 the others, four under the chin, and two on the snout behind the nostrils. Teeth in 

 two patches, acute and file-sliaped. Pectoral fins and tirst dorsal tin armed with an 

 antenor spine. First dorsal trapezoidal and before the abdominals; second oi)posite 

 the anal. Body compressed behind, vent posterior and sub-medial. Operculum sim^jle." 



By the above limitation, the subgenus Idalurus is seen to partly correspond with 

 that of Pimelodus of Cuvier, the teeth being said to be in two patches or only on the 

 jaws. By the description of the condition and position of the fins and the number of 

 barbels, it includes only a small section of the Ouvierian subgenus. 



The name Ictali(rus must be then reserved for some of our Siluroids — for all, if 

 they should be found to be congeneric— for a section, if it is ascertained that several 

 genera are embraced' under the subgenus. 



Our studies of the Siluroids have con^^nced us that there are four natural genera 

 found in the United States, three of which were included by Rafiuesque in his sub- 

 genus Idalurus, but placed at the same time in sections, which received from him 

 various scientific names. 



The sections established by Rafiuesque were chiefly characterized by the foi-m of 

 the "tail" or caudal fin, and of the eyes, and the number of rays in the abdominal or 

 ventral fins. 



The fii-st section was named Elliops, and included fishes with the "tail forked. 

 Eyes elliptical. Abdominal fins with less than nine rays." 



This group exists in nature, and is of generic value, but the characters given by 

 Rafiuesque are not those which essentially characterize it, nor can the name Elliops be 

 retained for it. 



The name given to a group as a whole must be preserved, and if that group is 

 di^■ided into sections, one of those sections must retain the name of the greater group 

 In Rafinesque's system, Idalurus is the greater grouji, and in it are included all the North 

 American Pimelodi, with the exception of Noturus. When Rafiuesque divided that 

 group into sections, he should, therefore, have still retained that name for one of them. 

 Such has not been done, but upon each of his sections was conferred another name. 

 As this is in opposition to the rules of nomenclature, Idalurus must be restored to one 

 of his secti6ns, and it is advisable to retain it for his first, and reject the name of 

 ElUops. The section with this name is now accejrted as a genus; its diagnosis will be 

 hereafter given. 



The name Pimelodus, it is true, was applied to all the Idaluri, and by that name 

 only are they called. If Pimelodus had been of Rafinesque's creation, that name 

 should, therefore, have been adopted; but as Rafiuesque has only taken it from La- 

 cepfede, with the characters given to it by jjs founder, it is to be supposed that he 

 intended it to be otherwise restricted. It a2)pears to us that it is no valid argmnent 

 against the acceptation of Rafinesque's names for genera, if his sections should prove 

 to be such, that he did not apply them specifically. 



The section called Elliops, on comparison with its type Pimelodus ccet-ulescens of 



