76 



SCANDINAVIAN FISHES. 



tlie b.ise of these fins and there become united into lai-ge 

 'tiiicovei's', though still maintaining their oblong, linear 

 form." In this idea of the progression of development 

 (metamorphosis) between the two genera, we may also 

 tind the explanation of tlie other differences between 

 tlicm. In Pterycombus the dorsal and anal tins are 

 longer and begin uearei- the head, l)ut this is also true 

 of the adult specimens of Bruma compared Avith the 

 younger. In the former genus tlie superior profile of 

 the l)udy .slopes uniformly in a slight curve from the 

 Itegiimiiig of tlie dorsal fin to the tip of the snout, 

 and tills is also true of the younger specimens of Brama, 

 in which genus the height of the forehead and the abrupt 

 slope of the snout become developed only later in life. 

 The spines on the scales which we have seen in Pte- 

 rijcomhus, are also represented in Brama, but are here 

 really to be regarded as evanescent groAvths. In other 

 respects the formation of the scales is essentially the 

 same in both genera; but the widening of the high 

 scales and their singular form, reminiscences of the 

 Ganoid type, are more marked in I'teri/comhiis and the 

 younger specimens of Brama. Thus in the develop- 

 ment of the dorsal and anal fins Pterycombus is more 

 ;i(l\anced than Brama, while in the other characters 

 mentioned above Pterycombus has stopped short at a 

 stage of development corresponding to the juvenile stage 

 in Brama. As in Pterycombus, the ventral fins are 

 also covered with scales in this genus, and in Brama 

 there also appears a row of singular scaly growths, 

 elongated into a spoon-shaped form, and situated in 

 the axil on a dermal flap which extends along the 

 inner base of the pectoral fin". The gill-openings are 

 also large in Brama, l)ut the In'anchiostegal membranes 

 ai-e united under the isthmus from about the middle 

 of the lower jaw. 



In the genus Brama 9 species have been distin- 

 guished among adult specimens, but the correctness of 

 ])erhaps most of them is still doubtful. In his meri- 

 torious treatment of this (luestion LCtkkn'' has pointed 

 out the character which may be derived from the dif- 



ferent number of rays in the anal fin. When we also 

 observe that the species, all West Indian, which are 

 distinguished by the shortest anal fin, also have the 

 hind margin of the caudal more or less curved in an 

 S-shape, while in the other species it is simple liut 

 deeply forked, we have here a ground for the distinc- 

 tion of at least two groups of forms within the genus. 

 This, however, does not preclude the possibility that 

 even the number of rays and the length of the anal 

 fin may also prove subject to such changes due to age 

 that the character derived therefrom may lose its 

 validity. HoAvever, as the same changes affect the dor- 

 sal fin as well, we naturallv obtain a surer test of the 

 character by comparing the Uvo fins with each othei-. 

 Even the number of roAvs of scales on the body may 

 be employed, at any rate in extreme cases, as charac- 

 ters for the species. But here we are met by the dif- 

 ficulty of counting these roAvs \\'ith uniformity and 

 excluding the more or less irregular laj'ers of scales 

 in front of the caudal fin and on its base. Lutkkn 

 remarks that if, Avith Gunther, we count along the 

 lateral line, ^ve find from 80 to 95 rows, but according 

 to Lunel's method of counting in a, straight line from 

 the upper end of the gill-opening, Ave find only from 

 70 to 76 rows in Brama Baii, the sjjecies in which 

 LiLL.jEBORG has counted from 70 to 80 rows. The 

 statements which are not accompanied b}' a clear ex- 

 planation of the manner of counting, thus lose a great 

 part of their value, especially as age seems also to 

 involve an increase in the number of roAvs of scales. 

 Among the forms of this genus tAvo Scandinavian 

 species have been distinguished, liotli Avith the base of 

 the anal fin more than 70 % of that of the dorsal: 



1: Base of the anal fin more than 40 % of 



the length of the body ; greatest height of 



the dorsal about -,'3 of the length of the 



head Br. Raii. 



2 : Base of the anal fin less than 40 % of 



the length of the body; greatest height 



of the dorsal almost C(|Ual to the length 



of the head _-. Br. loni^ipiiutis. 



" Fur the liKirpliologicnl significance of this deriiiiil flap see below on Cliiroliiphis galerita. 

 * ISpoliu .ML, I. c, ]j. 407. 



