278 ME. C. TATE REGAN OX EEESHWATEE FISHES 



The piinci[:al changes in structure that call for the recognition of so many genera 

 have been in the spinous dorsal fin, the scales, the gill-rakers, and the jaws and teeth. 



As above mentioned, the spinous dorsal fin is usually formed of a stout and 

 pungent spine followed by three to six slender and flexible ones ; the only exceptions 

 are Ehadinocentrus, with all the spines flexible, and Centratherina, with them all 

 pungent *. 



In Melanotcenia the scales are large, regularly arranged, with the edges entire or 

 slightly crenulated ; they are similar in structure and arrangement in all the other 

 genera except Glossole^ns, which has the scales smaller, irregularly arranged, and with 

 the crenulations very pronounced, having the appearance of a series of tongue-like 

 projections at the edge of each scale. 



In Melanotwnia the gill-rakers are of moderate length, and number 12 to 16 on the 

 lower part of the anterior arch ; all the other genera agree, except again Glossolepis, 

 which has longer, finer, and more numerous gill-rakers, about 30 on the lower part of 

 the anterior arch. 



In Melanotcenia the premaxillaries have a horizontal anterior expansion that forms 

 an angle with the oblique lateral rami and fits an emargination of the transverse 

 anterior part of the lower jaw ; the teeth in the jaws are conical or villiform, in bands, 

 with the outer series enlarged ; there is a transverse band of similar teeth on the vomer, 

 a few far back on the palatines, and a patch at the base of the tongue. 



Ehadinocentrus and Glossolepis are similar, except that in the former the palate 

 appears to be toothless, in the latter the teeth are rather stout and obtuse. 



In Anisocentrus the prtemaxillary expansion is reduced, the lower jaw is included, 

 and its outer series of enlarged teeth is implanted horizontally and separated by an 

 interspace from the inner band ; there are no other difl^erences from Melanotcenia. 

 CMlatherina and Centratlierina are similar in mouth-structure, but in the upper jaw 

 the teeth extend on to the outside, projecting from the thick lip, and in the lower 

 there is no interspace between inner band and enlarged outer series ; in the former 

 genus the palatine teeth, in the latter the vomerine teeth as well, are lost. 



lihomhosoma resembles Melanotcenia in having a well-developed anterior expansion 

 of the prfemaxillaries forming an angle with the lateral rami; but the lower jaw is 

 included, the bands of teeth extend on to the outside of the jaws, and there is no 

 marginal series of enlarged teeth. 



Si/nopsis of tlie Genera. 



I. Jaws equal anteriorly. 



A. Scales large, regularly arranged, with edges entire or slightly 

 crenulated. 

 Spinous dorsal witli the first spine stout and pungent, the rest slender and 



flexible 1- Melanoteenia. 



* Another example of the reconversion of flexible spines into pungent ones is the recently described 

 Trematomus ccntvonotiis (Regan, Ann. Mag. Nat. Hist. (8) siii. 1014, p. 12). 



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