during their Growth and Development. 5 



The primordial but transitory characters which distinguish 

 the young Holocentra and Myripristes are therefore : — 1. The 

 more or less excessive prolongation of the bones of the snout 

 in the form of a pointed beak, entire or cleft in two, with 

 denticulated edges, and comparatively as large as the sword 

 of the swordfish ; and 2. The colossal development of the 

 occipital and prseopercular spines, as also, in part, of those of 

 the operculum. These spines, however, soon disappear or 

 become reduced to more modest proportions, or to perfectly 

 insignificant rudiments. 



3. Teteagonurus. 



This very characteristic genus, which is thoroughly pelagic 

 and probably bathyphilous, inhabits the Atlantic, where it is 

 frequently found in the stomachs of large voracious fishes or 

 dolphins ; and young individuals are often taken by the net. 

 Tetragonurus atlanticus, Lowe, is certainly specifically iden- 

 tical with T. Cuvieri^ K. The differences they present are 

 in part purely individual, in part differences arising from age. 

 Young individuals (32-62 niillims.), leaving out of considera- 

 tion certain modifications in the relative proportions of the 

 parts of the body, which are mentioned in detail in the Danish 

 memoir, are distinguished (1) by the spinous or denticulate 

 opercular and prajopercular bones, and (2) by the different 

 character of the scales, which much resemble those of the 

 young swordfish, and have only a single sharp keel (tlie scales 

 of the lateral line, however, have two), which terminates in 

 two or three spines recurved backward, giving the young 

 Tetragonurus a rough or villous aspect. The youngest ex- 

 amples (16 millims.) have neither scales nor spines on the 

 skin ; and their ventral fins are extremely short, nay, even 

 rudimentary. I have also discussed the question of the place 

 to be assigned to Tetragonurus in the true natural system. 

 We shall seek in vain for indications of relationship with 

 Mugil or Atherina ; the proposition of Lowe and Swainson 

 to refer it to the Scomberoids is perhaps that which is most 

 in accordance with nature. 



4. XiPHiAS and Histiophorus (Tetrapturus) . 



The young forms of the Xiphioids are already so well 

 known, thanks especially to Dr. Giinther's communications, 

 that the series of small individuals of the two types that I 

 have had at my disposal do not enable me to add much that 

 is new ; nevertheless I have been able to carry the evolution 

 of the two groups a little further, to a phase which must be 

 very near the exclusion from the eg^. The two principal 



