8D2 



■SCAXniX.WIAN I'lSHES. 



r;iker!< itru scnttiTcd and slioi't, hut that, wlicrc tlic diet 

 is composed of siiiidl objefts, princip;tll\- KittiniKishdra, 

 they are finer, denser, and longer, thus forining a more 

 perfect filtering-apparatus. No\v as tiic diet is com- 

 Hionh' altered witii the age of the (Jwvniads, -we n\;\\ 

 as a rule expect to tind a corresponding change in the 

 gill-rakers". But Gwyniad forms occur, for example 

 tiie Sil)eriaii pelct (among the \'endaces) and iiiitksiiii 

 (among the true (iwyniads) or the so-called asp (jf Lap- 

 land, wliich attain a considerable size, but have per- 

 sistently dense and numerous gill-rakers. Some forms, 

 again, show an increase with age in the number of the 

 gill-rakers''. The variations do not therefore follo^^■ in 

 absolute succession the changes of growth. They rather 

 shoAvs a certain independence in their appearance, an 

 independence which in some forms has rendered them 

 available as characters, at least in their extremes, espe- 

 cialh' as thev are accompanied in most eases bv an 

 external character, a difference in the shape of the snout. 

 By the last-mentioned character tAvo groups have 

 long been distinguished within the genus Coiti/oiiiis, 

 one of them having its liest-l^nown representative in 

 our Vendace, the otjier in dur <i\vyniad. Td the for- 

 mer group Agassiz' gave the name of Argi/rosomus, 

 iharacterized essentially by the projection of the point 

 of tiie lower jaw ])evond the ti]i of tiie snout, \vhereas 

 tiie form-series of tiie true Gwyniads advances to a 

 greater development and i)rotrusion of the tip of the 

 snout, culminating in the form henee known as the 

 )t('ilihsik (Beaked Giriix'iad, ('(iref/oiuis (i.ri/rlii/iicl/iis). The 

 limit between the two groups it is indeed inipussible 

 sharply to define, on account of the transition forms; 

 but in its two extremes the altered shape of the snout 

 is due to a ver\- considerable difference in tlie form 

 and position of tiie intermaxillaries. We liave already 

 remarked in the case of 7'lii/iii((Ui(s a eonsidei'al)le re- 

 duction of tiie intermaxillaries, to small, flat and tliiii, 

 triangular disks, set transverseh' in fi'ont of the tip of 

 the snout and tiie incurved articular processes of the 

 maxillaries, slightly thickened at the lower margin 

 alone, where lie the alveoli of the single row of teeth, 

 which are dii'ected inwards (baekwarcls), more or less 

 \'erticall_y to the plane of the disk. In the \'endaces 

 tliis structure recurs, onh' that tiie teeth are as a 

 rule wanting, the disk is still thinner and rests more 



entirely on tlie front of the inward, terete tip of the 

 maxillary iione. This part of tlie maxillary bone some- 

 times, as in the Scandinavian ^'endace, bears outside 

 tiie jn-otuberance which articulates with the ethmoidal 

 cartilage, a separate process, directed downwards (for- 

 wards), with which the inner (iiind) surface of the inter- 

 maxillary bone articulates, and b^- means of which the 

 said bone is raised when tlie mouth is opened. The 

 lireadtii (height) of the interiiiaxillar\ lione does not 

 exceed "/r, of tlie breadtii of the snout across the ar- 

 ticular knobs of the maxillaries, and its sharp inferior 

 margin then forms the osseous framework in the sharj), 

 transverse margin of the tip of the snout. In tlie true 

 Gwyniads the internlaxillar^" bone on each side of tiie 

 snout is highei-, tiie de|ith of tlie snout being al\va\s 

 more than ^/,. of its breadtii atn-oss the iirticidar knobs 

 of the maxillaries, and more roliust, witli teeth or ru- 

 diments tiiereof in the above-mentioned position. It is 

 also more firmly articulated witli the under surface of 

 the tip (articular process) of the nlaxilial•^• lione. This 

 articulation is formed in tlie following manner: the 

 ujiper margin of tlie iiiteriiiaxillar\" lioiie is hollowed 

 into a groove which surrounds the said lower margin 

 of the maxillar\' not onlv in front, Ijut also more or 

 less far back (outwai'ds) on tiiat jinrt of the latter bone 

 whieii forms tlie upper lateral margin of the mouth. 

 The intermaxillar'\- l>one thus assumes a more vr less 

 vertical position wlien the mouth is closed; and when 

 the tip of the snout is jirolongated — which often ap- 

 ]iears as a change of growth — the under margin of this 

 bone is turned more and more in a backward direction. 



The scales of Coregonus are thin and cycloid, as 

 a rule thinner than those of the Grayling, with not very 

 distinct radiating grooves, though both the anterior and 

 posterior margins of the scales are generally corrugated 

 and notched thereby. The scales of the lateral line, 

 here as in the Grayling, commonly have the anterior 

 margin elongated to a triangle at the middle. 



The internal organs resemble those of the Salmons; 

 but the pyloric appendages are shorter and still mora 

 numerous (Kroyer counted about 200). The jierito- 

 neum is silver\- white. 



The genus has the same geographical extension a 

 the Graylings. It is most iiiuuerous, and apjiears i 

 its most developed forms, in the Siberian rivers, whic, 



" See for e.xttinple llie four Gwyniiul.*, 206 — 350 iniii. Icmg, wliicli nre incliuled in Smitt. lulfiii. Sahin 

 ' See for example Smitt, 1. c ji. 278, tlie .iverages for Coregonus Nihsonii and Cor. Wai-tniniuu. 

 <■ Lal-e S'ljienoi; y. 3.39. 



olr. X. Xi.s. 1711—173 



I 



