2?6 CLASSIFICATION OF FISHES. 



the other types, is rather short, so as not to exceed the 

 length of the dorsal. All these characters are pos- 

 sessed by the shads, which have merely a slight emar- 

 gination on the upper jaw, — a variation so slight, when 

 compared to numerous others in this group, that we 

 cannot possibly adopt the sub-genus Alosa*, or rather 

 Clupanodon ; for the latter name has the priority of the 

 former by many years. From these to Chatoessus the 

 transition is very gradual ; the change consists in the 

 prolongation of the terminal ray of the dorsal, which 

 exceeds the others so much as to become twice or thrice 

 their length. These fish are generally much broader than 

 the herrings, as in C. thryssa \: the relative size and 

 position of the dorsal and ventral fins are the same as in 

 Clupea; but the anal fin is considerably longer, and the 

 mouth usually much smaller. They are all natives of 

 warm seas, chiefly of India. In two or three, a remark- 

 able deviation from the usual equality of the jaws is 

 observable : the snout or point of the upper jaw projects 

 beyond the under, — a deviation of structure which can 

 only be explained when we look to the singular herrings 

 forming the sub-genus Thryssa ; this group is a very 

 remarkable one on many accounts. In the first place it 

 has an obvious alliance to the anchovies, upon which 

 account Cuvier has placed them following each other, — 

 a station which we shall subsequently show is truly na- 

 tural : this affinity is indicated by an excessively wide 

 mouth ; the edges of the jaws, particularly the upper, 

 or rcaxillaries, being sometimes armed with a single 

 row of short, isolated, acute teeth : these, however, must 

 not be considered as a primary character, because they 

 are sometimes wanting ; while in other species, as 

 Thryssa Hamiltonii Gray^, they appear distinctly de- 

 fined; the tip of the snout, also, is sometimes, as in the 

 last species, rather advanced over that of the lower jaw, 

 similar to what we see in the anchovies, while in others 



* if sucn deviations of structure are sufficient for sub-genera, that of 

 Thryssa alone might furnish five or 6ix of equal value, 

 f 'Bloch, pL 404. X Ind. Zool. vol. ii. pL 22. -fig. 3. 



