CLUPEA; THE SUB-GENERA. 277 



the mouth is nearly as vertical as in Pristogaster. Now 

 the question is, How can these deviations of structure be 

 explained ? and what affinities do they indicate ? The 

 advanced snout of Chatoessus nasus and latus, seems to 

 prepare us for the same structure in some of the Thryssce, 

 while the more vertical mouth of the typical species of 

 Thryssa plainly intimates, we conceive, that the next type 

 which follows in the series is Pristogaster. The cir- 

 cumstance, again, of some of the Thryssce. having teeth, 

 and others none, is at once accounted for, when we 

 recollect that it is through this group we pass from 

 the toothless herrings, or Clupea, to the salmon-herrings, 

 or Elops. This variation, therefore, must consequently 

 happen, because it is precisely in this part of the series 

 that the teeth began to appear. Cuvier has simply ob- 

 served of Thryssa, that it only differs from the anchovies 

 with serrated bellies by the greater prolongation of their 

 maxillaries. This is such an indefinite character, that 

 we have placed all the serrated anchovies in Thryssa, 

 leaving only such as have the belly smooth (like the 

 European) in Engraulis. Thryssa is further dis- 

 tinguished from Clupea and Chatoessus by the position of 

 the ventral fins : these, instead of being placed under 

 the dorsal, are situated before it, and are so small as only 

 to be half the size of the pectorals ; thus, again, we 

 are prepared for Pristogaster, where these fins totally 

 disappear : the mouth is still more vertical, or, rather, it 

 is completely so ; while the dorsal fin, which is very 

 short in Thryssa, is now so much reduced, as, in one 

 instance, to be totally wanting.* The Indian species of 

 Pristogaster are oblong or lengthened fish, while those 

 of the Atlantic are short and broad: these latter, we 

 suspect, are the true types ; since the deep, prominent, 

 and arched belly, which is the chief character of these 

 fishes, is more developed in the American than in the 

 Indian species : the mouth, as just observed, is com- 

 pletely vertical ; and this, with its small size, and its 



* Aptert/gia, Gray, Ind. Zool. u 



T 3 



