32 bulletin: museum of compaeative zoology. 



The general outline of body in this species is more suggestive of Acanthurus 

 than Pygaeus, but the fin-structure is wholly in accord ■with the latter genus. 

 The development of the spinous dorsdl is about equal to that of the type 

 species of Pygaeus, but the articulated dorsal is less strongly developed. This 

 is a character of specific importance, and its variation amongst different forms 

 belonging to the same general group is indicated by the following formulae : 



Pygaeus holcanus D. 10 or 12 + 20 {Jide Agassiz). 



" agassizii D. 10 + 9 ; A. 5 + 8. 



" nohilis D. 12+ 12; A. 3 + 12. 



" coleanus D. 14 H- 15 ; A. 9 + 11. 



Acanthurus gaudryi D. 7 + 28 ; A. 3 + 25. 



" tenuis D. 9 + 21 ; A. 3 + 19. 



LOPHIIDAE. 



Histionotophorus, nomen nov. 



[Histiocephaltis A. de Zigno, 1887.] 



The name proposed for this genus by Baron de Zigno is not only inap- 

 propriate but preoccupied, Diesing having applied it to a genus of Vermes 

 in 1851. The title Histiocephalus may therefore be discarded in favor of 

 Histionotophorus, which is bestowed in allusion to the sail-like median fin ex- 

 tending along the back. 



Histionotophorus bassani (Zigno). 



(Plate 1 , Figs. 1-3 ; Text-fig. C.) 



1887. Histiocephalus bassani A. de Zigno, Mem. R. Istit. Veneto, xxiii. p. 31, Fig. 9. 

 D. I - I - I + 13 ; C. 8 ; A. 9 ; V. 7 ; P. 6. 



A comparatively small pediculate species attaining a total length to the 

 base of the caudal fin of about 6 cm. Mouth oblique, maxillary extending far 

 downward, dentary thickened, jaws with cardiform teeth, skin naked. An- 

 terior dorsal of three separated tentacle-like spines on the head, posterior dorsal 

 high, much extended, with thirteen articulated rays, the fin-membrane stiffened 

 at the base with small spiniform calcifications. Pectoral members situated 

 immediately above the origin of the anal fin, their short rays directed vertically, 

 and supported by extremely long pseudobrachia, which are apparently composed 

 of two actinosts. Number of vertebrae apparently not more than 18 (according 

 to de Zigno, however, there are 22 in the type, 10 abdominal and 12 caudal). 



Three specimens answering to the above description, two of them in counter- 

 part, are preserved in the Museum of Comparative Zoology, and their princi- 



