278 CLASSIFICATION OF FISHES. 



toothless jaws, separates Pristogaster both from Thryssa 

 and Engraulis. The absence of teeth, again, indicates 

 a return to the typical form of Clupea. But there is yet 

 another modification of form which is necessary to effect 

 this union. This is seen in certain herrings which have 

 all the characters of Pristogaster, except that they have 

 a remarkably small ventral fin — so small, indeed, that 

 it may be considered rudimentary : to these we give the 

 name of Platygastcr. In some, as in P.verticalis*, the 

 mouth is completely vertical ; in others it is less so 

 (P. Africana t) ; while in some, which approach the true 

 herrings, the mouth (as in them) is only oblique. As the 

 progress of this transition from Pristogaster to Clupea, 

 through Platygaster, is not only particularly beautiful, but 

 highly important to our present purpose, we shall call 

 the attention of ichthyologists to the steps by which it is 

 effected; for it fortunately happens that this can be done 

 by the aid of the figures of such species as have already 

 been published. In the first place, let the reader turn 

 to the 192d plate of Russell's Indian Fishes, where he 

 will find, at fig. 2., our Pristogaster elongata (Tardoore 

 Russ.), a fish which Cuvier himself cites as one of the 

 types. Now the figure immediately above this (Platygaster 

 vertical is Sw.) is absolutely a Pristogaster in its form, 

 its vertical mouth, and its long anal fin ; while it is a 

 Platygaster in its very small ventral fin, placed a little 

 before the dorsal : the position, also, of this latter fin is 

 more towards the middle of the back than in Pristogaster 

 elongata; and thus it agrees with Clupea, The very 

 same structure is seen in Platygaster macropthalma 

 Sw. % We then, in P. affinis§, get the typical structure; 

 the minute ventral fin being nearer to the pectoral 

 than to the dorsal, and the mouth less vertical than in 

 the two former species. Platygaster Africana \\ leads 

 us a step nearer to Clupea, the ventrals being rather 

 nearer to the line of the dorsal than to the pectoral. This 



* Russell, pi. 192. f Clupea Africana, Bloch, 407. 



t Iangarloo, Russell, pi. 191. \ Clupea affinis, Grav, Ind. Zool. 



I! Clupea Africana, Bl. pi. 407. 



