GENERA OF SALMONID^. 9 



No one external or internal characteristic will alone distinguish the Salmonidae. 

 The other salmonoid families are: the Coregonidse, which comprise the whitefishes and 

 ciscoes; the ArgentinidcE, which include only a single species, the silver smelt {Argentina 

 silus), known as the sea smelt and king herring, and the Osmeridse, which include the 

 anadromous marine and fresh water smelt {Osmerus) and the marine capeUn {Mallotus). 



These are the most salient, family differences, and it is seen that there is one charactei- 

 that distinguishes Salmonidse from all other famiUes mentioned. In fact no other family 

 of teleosts has yet been observed to possess it. That is the ventral mesentery. However, 

 this exception does not detract from the previous general statement that no one char- 

 acter usually enumerated as the chief characteristic of the salmon will alone distinguish 

 it from all other families.' As now restricted, the family Salmonidse of New England 

 comprises only the salmons, trouts, and chars, which previously constituted the sub- 

 family Salmoninae. The Coregonidse comprises the whitefishes and ciscoes; the Argen- 

 tinidse but one species, the silver smelt {Argentina silus), known to New England fisher- 

 men as 'sea smelt' and king herring; and the Osmeridae includes the anadromous, marine 

 and fresh-water smelt {Osmerus) and the marine capelin {Mallotus). The C6regonid8e, 

 Argentinidse, and Osmeridae in many ways are more closely related to each other than 

 to the Salmonidaj. Argentina is the most highly specialized form and doubtless repre- 

 sents the end product of an early diverging line from common isospondylous stock and 

 is not closely related to the Salmonidse. It possesses a well-developed, spiral valve in 

 the intestine (Kendall and Crawford 1922, p. 10). 



Genera of Salmonidae. 



According to Linnseus (1758, p. 308-312) the salmon family comprised only one 

 genus {Salmo), although by subdesignations the Ust of species is subdivided as Truttse, 

 Osmeri, Coregoni, and Characini. By later writers these divisions were transcribed into 

 the smgular, Trutta, Osmerus, Coregonus, and Characinus as used by Artedi and pre- 

 viously by Linnseus and accepted as generic names, credited to Linnseus. The division 

 Truttse comprised 24 species of which only 17 are now recognized by any ichthyologist 

 as belonging to the Salmonid^, and Americans admit only 15 to the family and 6 to 

 the genus Salmo. 



Regan (1914, p. 407) has shown that the genus Oncorhynchus must be relegated to the 

 synonymy of Salmo, or else the Pacific trouts now regarded as Salmo must be included 

 in the genus Oncorhynchus. Regan appears to be correct as concerns the cranial char- 

 acters upon which he bases his conclusions. But he seems to be in error as concerns the 

 anal fin-ray character, since the supposed Oncorhynchus masou, which he found to have 

 the few rays of Salmo, has been shown to be a Salmo (Kitahara 1904, p. 1 18-120, and 

 Jordan 19055). Furthermore the number of anal rays is not the only distinctive character 

 of Oncorhynchus. 



'Since this statement was written it has been found that Weber (1886) says that the intestine of Coregonus oxyrinchus is 

 attached posteriorly to a ventral mesentery. From what he says of C. lavaretus it is inferred that it also was found to have 

 a ventral mesentery. Kendall (1921, p. 197) found none in Coregonus clupeaforrnis. 



