duriag their Growth and Deaelo2)meat. 7 



Xiphias observed, 10 millims. in length. In contrast to this, 

 all the young Histiophori^ from 5^ to 100 millims., are com- 

 pletely naked and destitute of scales. Thus we cannot com- 

 pare with the scales of the young Xiphice those of the adult 

 Histiophori and Tetraptm-i, which are perfectly homologous 

 with those of the Thynnoids. The young examples of X. 

 fjladius^ from 37 to 57 millims., are adorned with transverse 

 bands, like many other small Scomberoids ; the frontal mar- 

 gins and the prseoperculum are denticulated ; and the latter is 

 also, in the youngest individuals, furnished with a group of 

 spines, as in many other young Scomberoids. We never find 

 in them any traces of ventral fins, whilst these are never 

 wanting in the Histiophori^ and always occur, in a rudimentary 

 state, even in the youngest. Then, in the youngest Xiphias^ 

 the head is flat without presenting the sudden depression of 

 the forehead which characterizes the Histiophori^ the rostrum 

 is shortj and broad at the base, and the mandible as long as 

 the upper jaw. Finally, the Xiphice, in all their successive 

 stages, present nothing comparable to the occipital and praj- 

 opercular spines, so enormously develojjcd in the young His- 

 tiophori^ and which resemble those of the Dactylopteri. 



It would be far from natural to exclude the Xiphioids from 

 the great family Scomberoidei, in which they And their most 

 strongly marked affinity in the genus Acanthocyhium {vide 

 infrh, p. 12). The more detailed classification of the 

 Scomberoidei has still to be settled. As to ranging them 

 with Cottoidei (" Cotto-Scombriformes ") I have never been 

 able to convince myself that there was any thing just and 

 natural in that classification. 



5. Trichiurus and Gempylus. 



Under the denomination of Trichiurid^ Dr. Giinther has 

 united two tribes wliicli are certainly related in a certain 

 degree, but which nevertheless are clearly distinguished from 

 each other. These are the true Trichiuridffi {Trichiurus^ 

 Lepidopus, Aphanopus, and Euoxymetopon) and the Gempy- 

 lidse or Thyrsitidai {Gempylus^ Prometheus^ Epnnnula^ Nesi- 

 archus,Nealotus, and Thyrsites). The latter must be united 

 with the Thynnidaj, but may nevertheless form a secondary 

 group among them. 



With regard to the genus Trichiurus I will, in the first 

 place, remark that the species that it includes at present do 

 not all appear to me capable of being maintained ; but I shall 

 not pronounce a definite opinion upon this point, as the mate- 

 rials at my command are insufficient. It is evident that the 

 two types represented by T. lepturus and T. muticus difier 



