SALMONS AND CIIAUUS. 



839 



and N. tnittd. Now hyliridisiu duos not iic'ci'ssaril)- in- 

 volve sterility; and \\itli regard to the Silver Salmon 

 and similar forms, it may well he difficult to determine 

 in each case whetliei- it is an altered manner of life — 

 a longer stay in the sea or large lakes — or h\l)ridisiii 

 that has brought about the said ciianges of form. But 

 it appears to be demonstrated that these changes attend 

 either or l)oth of the above conditions. 



In Sweden and, generally speaking, in all temperate 

 countries, the Cliarrs are true fresh-water tishes; but 

 such is not the case in the arctic parts of their geo- 

 graphical range. There the\' live like the Salmon; Es- 

 mark" and Hethng'' found them in the Arctic Ocean 

 off Nor^vegian Fiiuimark, and off Spitzbergen they are 

 the favourite food of the Beluga {Iklphmapterus lettcas), 

 which follows them to the head of the gulfs and bays. 

 Ill the sea thej- wear the colours of Silver Salmon, 

 and do not ac(|uire their ])i'oper Oharr drQSS before 

 entering the rivers. 



Characters both of form and colour indicate in 

 their variations a close relationship between the Sal- 

 mons. Their differentiation seems to be of late origin, 

 and they should perhaps be regarded as species which 

 are still developing constancy of characters ^ 



The skeleton of the Salmons is feebly ossified in 

 sharp contrast to that of the preceding family. The 

 cranium is for tiie most part persistently cartilaginous, 

 and most of its bones lie as separate covering-bones 

 on the almost continuous capsule of cartilage. The 

 occipital ridge is merel}' a short terete process, extend- 

 ing about as far back as the ordinary processes from 

 the mastoid (epiotic) and squamose (pterotic) bones. 

 The posterior oculo-muscular canal is large, and pe- 

 netrates the occipital region behind, being covered 

 below by the parasphenoid bone, which is strongly 

 bent in the sphenoidal region, and centrally divided 

 in front by the Y-shaped basisphenoid bone, which is 

 wanting in the preceding family. Here, on the otiier 

 hand, as in the following genera, there is no pha- 

 ryngeal process. The orbits ai'e separated internally 

 by a thick wall, composed of cartilage and the orbito- 

 sphenoid bones. The osseous framework of the upper 

 jaw, as we have mentioned above, is quite different 

 from the corresponding structure in the Cyiirinoids. 



Tlie niaxillaries ai'ticulatc in frcjrit, like the intermaxil- 

 laries and the palatine l)ones, and dose l)etween these 

 two pairs; with the cartilaginous rostral part of the 

 cranium (the rostro-ethmoidal cartilage). But they 

 Innc iiiidi'i-gone considei'able elongation — the inter- 

 maxillaries, on the other hand, are comparatively short 

 — and arc furnished with teetii, as well as the inter- 

 maxillaries and the palatine bones. Their anterior part 

 is, however, covered below by the intermaxillaries, so 

 that their externall)' \'isible length — as it is given in 

 the above definition of the genus — is measured from 

 the hind extremity of the latter bones. Above their 

 posterior part lies the covering-bone {os siippJementare) 

 which ans\vers to the cheek-bone {os jufjale) of the 

 higher vertebrates. The vomer is set as a covering- 

 bone on the middle of the under surface of the rostro- 

 ethmoidal cartilage and on the anterior extremity of 

 the parasphenoid bone. In the Salmons its shaft (body) 

 is fairl}' long and broad, carinated on the under (outer) 

 surface, but thin; in the Scandinavian Charrs, on the 

 other hand, ossified hardly at all or only on the sides. 

 The dentition of the vomer is also confined, as a rule, 

 in the latter to the anterior part, the so-called head; 

 while in the Salmons it extends, at least during youth, 

 to the shaft as well, but is generally more and more 

 reduced with age. The other bones of the palate, ex- 

 cept the palatine bones proper, are toothless in this 

 genus. The pterygoid bones are slender and curved in 

 the ordinary manner to unite the palatine and quadrate 

 bones. Within them lie the raesopterj^goid bones, which 

 are thin, Imt broad behind, and form the gi-eater part 

 of the roof of the mouth. According to Lilljeborg 

 these t^vo bones afford a constant distinction between 

 Trout and Salmon. In the former, he says, their breadth 

 decreases from their middle point even in a backward 

 direction, whereas in the latter they grow broader all 

 the way from the anterior to the posterior extremity. 

 A great difference from the preceding family appears 

 in the branchiostegal membranes, which are fur- 

 nished with a far greater number of rays (9 — 12, in 

 exceptional cases 8 or as many as 14, in Oncorhyn- 

 chiis sometimes 16). These rays are, however, of the 

 same broad, blunt, sabre-like form as in the Cj- 

 prinoids. 



" Sk-and. Xaturf. Mode, Chrnia 1868, Forh.. p. .527. 

 ' Smut, 1. c, tab. metr. VI, No. 399. 



"■ "In numerous cases cue is much tempted to ask whether we have not to deal with a family which, being one of tlie most recent 

 creation, is composed of forms not yet specifically differentiated": GIInther, Cat. Brit. Mus., Fish., vol. VI, p. V (preface). 



Scatidinavian Fiahes. 10^ 



