406 



SNODGRASS AND HELLER 



length, and has a shape very similar to that of Valenciennes's figure of 

 Xesurus laticlavius, while others duplicate in every way the type 

 of Xesurus clarionis Gilbert & Starks. These 2 extremes certainly 

 have a very different appearance, but our specimens show a closely 

 graded series of differences from one to the other. Since this is the 

 case we recognize only one species, X. laticlavius by priority. 



The pectoral fin varies much in shape ; in some the posterior margin 

 is almost straight, in others the tip is conspicuously bent backward. 

 The greatest depth of body is generally much in front of the middle, 

 being at the vertical through base of ventrals, or even in front of this 

 in specimens of least depth. In small specimens (23 mm. long) the 

 spines of the lateral caudal plates are proportionally smaller than in 

 adults, the anterior angle not elevated nor produced forward, and the 

 margin serrate. On most of the smaller specimens there are only 

 slight traces of spine-bearing plates in front of caudal peduncle ; on 

 the large specimens such plates are large and prominent; caudal 

 lunate with median rays the length of the ventrals, the lower lobe 

 often longer than upper. In most specimens the lateral line is dis- 

 tinct, in others of the same size it is entirely lacking. 



Most of the variations described above are not dependent on age, 

 nor has the locality or the season any influence in their production, 

 for we found all extremes in specimens of the same size, taken at the 

 same time at the same island. 



MEASUREMENTS AND FIN RAYS OF XeSUTUS 



Family BALISTIDJE. 



138. BALISTES VERRES (Gilbert & Starks). 



Pachynathus capistratus, JORDAN & EVERMANN, Fishes North and Mid. Amer. 

 n, 1704, 1898. JORDAN & MCGREGOR, Rep. U. S. Fish Comm. for 189! 

 (1899), 280 (Revillagigedo Islands) ; not of Shaw. 



