346 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



vol. 48. 



plate more freely movable, each lateral prolongation terminating in a short 

 free spine. Small plates present on gill membranes and on gular membrane. 

 Gill membrane without free fold. Two maxillary barbels. Small blue spots 

 present on head and anterior part of trunk. Dorsal fins without dark bars at 

 base or tip triacanthits. 



XENERETMUS LATIFRONS (Gilbert). 



The principal distinctive characters of this species have been indi- 

 cated in the preceding key and in the comparison with X. leiops. 

 The following may be added: 



The anterior 5 or 6 plates of lower lateral series spineless; ventral 

 series becoming spineless from 1 to 4 plates in front of origin of anal 

 fin. Patch of vomerine teeth wide, crescentiform, the posterior mar- 

 gin concave; palatine bands wider than those in the jaws. Sides 

 with faint traces only of darker bars. Inferior surfaces whitish 

 throughout, the lower side of tail not dusky. No bright spots. 

 Spinous dorsal with a well-defined jet-black margin of uniform width 

 throughout. Rays of soft dorsal and caudal dusky, a narrowly ellip- 

 tical patch of the membrane bordering each ray dusky in the distal 

 half of the fins. Posterior part of buccal cavity blue-black. 



As is usual in this group, there are two pairs of plates on breast 

 in front of the base of ventral fins. In addition, there is a small 

 unpaired plate which varies in position, being sometimes wholly 

 posterior to the paired plates; sometimes farther forward interposed 

 between the plates of the posterior pair. 



In a young specimen 44 mm. long the breast plates are elevated 

 centrally and bear each a short spine. The vent is more poste- 

 riorly placed than in adults, being but little in advance of the tips of 

 the ventral fins. Beginning immediately behind the ventrals is a 

 double series of 12 small plates, each bearing a central prominence. 

 With increasing age the vent passes forward between these two 

 series. 



The cheeks are normally without plates; two specimens only of 

 the many examined had each a single plate on one side below the 

 suborbital ridge. 



In 26 specimens examined the fin-rays vary as follows: 





Dorsal spines. 



Dorsal rays. 



Anal rays. 





VI VII 

 6 20 



6 7 8 

 1 23 2 



7 8 

 23 3 







The median plates on caudal peduncle are as follows in 24 speci- 

 mens: 





14 

 6 



15 

 16 



16 

 2 







