chiosti'ii'al a]i|i:ir;itiis differs from that of llii' SnliuDiis in 

 its f'rwcr ra\s, 7 or at most 8, the anterior needie- 

 sliiuieil, the hist three I)roa(l and ensiform. The ojiei- 

 cular annaratiis is distinn'uished i'roin that of the Sai- 

 nious iirinei|iall\' li\' the fact that tiie iireoyiercidum is 

 nttaclied tu the uiiper part of the ludmaiidihular l)()ne 

 (wiiieh is iiere elongated in tlie form of a l)acl;\\ard 

 nroeess) iin]\- at tlie very top, in common with the ar- 

 ticular knol) of the operculum. IJelow the said process 



A 



Fig. 218. A, Scale from the lateral line o£ Osmenis cperlaniis with 

 imperfectly closed duct, magn. 8 diani. For the further elucidation 

 of its structure are added a scale (B) from the lateral line of a 

 Salmo triitta (9 338 mm. long, from Norrkoping), also magnified 

 8 diameters, and a section (6^) of 2'/, scales (magn. 10 diam.) from 

 the lateral line of a large Salmon, t, duct of the lateral lino; asq, 

 anterior part of the scale; psq, posterior part thereof; ji, pore in tlie 

 scale (answering to the deep incision in the scale from the lateral 

 line of tlie Smell), through which the nerve of the lateral line passes 

 from one scale to the next, after sending out a ramification with 

 a sensory organ into the duct on the outer surface of the posterior 

 part of the scale. 



is a large opening l)etween the jireopereultmi and the 

 hyomandibular l)one, which in front, on the other hand, 

 expands into a disk, forming a stronger support for 

 the j)alatine arch, and is itself strengthened by a down- 

 ward ridge at the middle of its inner surface. The 

 spinal column is similar to that of the Salmons; but 

 the hiemal arciies are not completely closed until they 

 reach the beginning of the caudal part. The .series of 

 bones wiiieji in the Salmons forms the postclavieular 



Ts. 805 



ap|)aratus, is iici'e re]iresented Ijy a small, round and 

 thin, disi<-shaped Imne ;i1 the jiiiid inferior e.Ktrcmity 

 of tiu> ejavich', with its upper pai't attaciied inside the 

 lower angle nf the posteriorly expanded disk of the 

 latter. Tlie pehic bones are weak and resemble those 

 of tlie Sidmons. 



Tlie scales of tiie Smelts are thin, on the sides of 

 the body elliptical, with longitudinal axis set crosswise 

 (up and down), on the belly more rounded or of broad 

 oval sliajie. In texture tliey resemble the scales of the 

 Salmons, without radiating grooves, but with more or 

 less niuiieroiis and dense concentric; strife. The indi- 

 stinct nucleus is eccentric and lies in the anterior (in- 

 serted) part of the scale. The lateral line is distinct 

 onh' on the ;interior part of the sides. Its scales are 

 deeply cloven lieliind, where the canal of the lateral 

 line has its course, and the duct belonging to each 

 scale, and surrounding the canal, in front of this cleft, 

 and on the outside of the scale, is open or at least 

 imperfecth' closed — as in the earlier developmental 

 stages of more com])lete lateral lines — the margins of 

 the primitive canaliculate duct not coalescing, even 

 where one of them overlaps the other (fig. 218, A). 

 The scales of the Smelt are further distinguished by 

 the absence of the layer of silvery pigment which else- 

 where lines the scales where this colour appears. The 

 silvery lustre is indeed present in a longitudinal band 

 along the sides of the Smelt; but on removing the 

 .scales ^ve distineth" see that the coat of pigment lies 

 in the skin under the scales. 



The relation to the Salmons has already been ex- 

 pressed in the above generic characters. But this re- 

 lation, as paleontology seems to indicate, is probably 

 one of development as ^vell, Osmerus standing nearer 

 to the common ancestors of the genera. This appears 

 most clearh' on a comparison of the average figures 

 expressing the corresponding relations of form in the 

 two genera. 



From tlie above table of averages (p. 8.53) we 

 easil\- see that the position of the dorsal fin, expressed 

 in the distance from the tip of tiie snout to the l)e- 

 ginning of the base of this fin, becomes more forward 

 with age — and the averages for the several ages show" 

 that this alteration of growth is greatest during the 

 earlier and earliest stages. The said distance decreases 

 botii in iiroiiiirtiun to the lenyth of the body and to 



Cf. Smitt, Siksinuseets Salmoiiider, pp. 11 and 25. 



