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 Pomucentrus arcifrons. 



Catalogue No. 

 Leland Stanford Jr. Uni- 

 versity Museum. 



Length in mm 



Depth 



Head 



Pectoral 



Ventral 



Eye: Head 



Preorbital : Head 



Interorbital : Head 



Dorsal Spines 



Second Dorsal Rays... 



Second Anal Rays 



Scale Rows 



Scales on Lateral Line .. 



(Type) 

 6356. '"94. 



115 

 57 

 30 

 29 

 32 

 27 

 22 



35 

 XII 



15 

 13 

 25 

 20 



no 

 58 

 29 

 28 



34 

 28 



34 

 XII 



15 

 13 

 24 



52 



49 

 32 

 30 

 36 

 33 



25 



34 

 47 

 32 

 30 

 39 

 34 



27 



24 

 43 

 33 

 27 

 31 

 34 



24 



The species of Pomacentrus living along the mainland of Central 

 America is P. rectifrcenitm 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. 



p1. viii. 



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

 Tagus Cove, Albemarle Island. 



Descriptioti of the Type. — Length 200 mm. Body ovoid, deep, 

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



