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Royal Society :■ 



firm, and to add the following genera in which I find the same thing 

 to occur; viz. — Hydrocyon, Alepocephalus, Macrostoma, Bisso, Pia- 

 buca, Serrasalmo, Xiphorhamphus, Tetragonurus, Salminus, Chal- 

 cinus, Pygocentrus, Labeo, and Catostomus. But, besides the 

 instance of Sudis and certain Siluroids above referred to, I find that 

 many other Physostomi have true bone-corpuscles in their scales ; 

 not only those of the lateral line, but all of them. From the results 

 of my examinations up to this time, which, however, on account of 

 the want of materials, are by no means complete, I am able to make 

 out the following list : — 



1. Characini. 



Of this family I have had the means of examining nearly all the 

 genera, including forty-one species. 



Characini with bone-co?pnscles in all their scales. 



Erythrinus unitaeniatus, Spix. 

 ErytHrihus microcephalus, Agass. 

 Macrodou trahira, J. Mull. 

 Macrodon auritus, Vul. 

 Pacu taeniurus (Prochilodus taeni- 



urus, Val.). 

 Pacu nigricans, Spix. 

 Pacu lineatus, Val. 

 Distichodus niloticus, Mull. Tr. 

 Alestes dentex, Mull. Tr. 



Anodus cyprinoides, Mull. Tr. 

 Auodus edentulus, Agass. 

 Anodus leucos, de Fil. 

 Scliizodon fasciatus, Agass. 

 Chilodus punctatus, Mutt. Tr. 

 Rhaphiodon (Cynodon) viilpihus, 



Agass. 

 Leporinus fasciatus, Mull. Tr. 

 Leporinus elongatus, Val. 

 Citharinus latus, Ehr. 



Characini without bone-corpuscles in their scales. 



*Hydrocion Forskahlii, Cuv. 

 *Piabuca bimaculata (Hyrtl. misit). 

 Gasteropelecus sternicla, Bl. 

 Gasteropelecus securis, de Fil. 

 Cheirodon Girard, nov. sp., dk FU. 

 Brycon falcatus, Mull. Tr. 

 Brycon, nov. sp., de Fil. 

 Serrasalmo rhombeus, Cuv. 

 :;: Serrasalmo marginatus, Val. 

 Xiphorhamphus falcatus, Mull. Tr. 

 *Xiphorhamphushepsetus,AfttW.7V. 

 Myletes rubripinnis, Mull. Tr. 



Myletes rbomboidalis, Cuv . 

 Tetragonurus mexicanus, de FU. 

 *Tetragonurus argenteus, Art. 

 •Tetragonurus maculatus, Midi. Tr. 

 *Salminus Orbignyanus, Val. 

 *Chalcinus Miilleri, de Fil. 

 Pygoceutrus nigricans, Mull. Tr. 

 Epicyrtus gibbosus, Midi. Tr. 

 Piabucina erythrinoides, Val. 

 Exodou paradoxus, Mull. Tr. 

 Leporinus, spec. 



With regard to the members of the second division, it is to be 

 observed, that probably in all of them the canals attached to the 

 scales of the lateral line are formed of true osseous tissue ; in those 

 marked with an asterisk I have found this by actual examination. 



The Characini are thus divisible into two groups, according to the 

 nature of their scales ; at the same time, these are not to be regarded 

 as natural divisions in other respects, and the less so as one and the 

 same genus, such as Leporinus, for example, may include species 

 which differ in the composition of their scales. The presence of 

 corpuscles, though connected partly with the size of the scales, does 

 not depend solely on this, for they may be wanting in large scales 



