204 



HELLER AND SNODGRASS 



dorsal disappears and the lips become pale-colored, while the orange 

 color of the posterior parts retreats backward until the individual is 

 about 50 mm. long, when it is confined to the posterior half of the 

 caudal peduncle. Later the orange color becomes spread indefinitely 

 over the posterior half of the body, differing in extent in different indi- 

 viduals, but it generally does not cover such a distinctly defined area as 

 in the young. Towards maturity the profile of the head becomes very 

 steep and convex before the eyes, in some individuals almost vertical. 

 A large series of this species taken at the Galapagos Archipelago 

 and at Cocos Island. 



MEASUREMENTS OF Pomacentrus arcifrons. 



The species of Pomacentrus living along the mainland of Central 

 America is P. rectifrcenum shown in Figure 2 of Plate v. It has been 

 reported from the Revillagigedo Archipelago, but the specimens are 

 probably young individuals of P. redemptus. 



Nexilosus gen. nov. 



Characters. Teeth incisor-like, entire ; suborbital adnate to 

 cheek ; no scales on preorbital, scales on suborbital not well formed ; 

 fourth gill opening a very small round aperture. These are all 

 Hypsypops characters except the adnate condition of the suborbital, 

 which is a characteristic also of Nexilarius. 



NEXILOSUS ALBEMARLEUS sp. nov. 



pi. viii. 



Type. Cat. No. 6359, Leland Stanford Jr. University Museum. 

 Tagus Cove, Albemarle Island. 



Description of the Type. Length 200 mm. Body ovoid, deep, 

 compressed; depth a little more than two in length; profile from 



