514 PROCEEDINGS OF THE NATIONAL MUSEUM vol.86 



pigmented. Three small spots remain of the blotch of pigment that 

 covered the base of the caudal in the smaller specimens. The body 

 is otherwise ^^dthout pigment. Although the digestive organs have 

 become enlarged so that the depth of the body anteriorly approaches 

 that of the adult form, the enlargements of the bases of the dorsal and 

 anal fin remain transparent so that this fish appears to have the 

 characteristic slender body of the smaller specimens. Whereas in the 

 case of the 12 mm specimen the pectoral and ventral fins were well 

 separated and the raj^s of the pectoral did not reach to the base of 

 the ventrals, in this specimen the base of the ventrals lies only a short 

 distance behind the bases of pectorals and the rays of the pectoral, 

 when depressed, extend nearly to the base of the anal. The ra3^s of 

 the ventrals have become even more elongate and reach to the first 

 rays of the caudal fin. Although the flexures of the intestine are 

 obscured by the dense pigment of the peritoneum, it is apparent that 

 the anus has moved farther anteriorly until it lies anteriorly to the 

 posterior flexure of the intestine. It is considerably nearer a vertical 

 from the base of the ventral than the origin of the anal. The scales 

 have not yet formed. 



Length without caudal 25 mm. Proportions of the length without 

 caudal: Length of head 2.3; snout to origin of dorsal L3; snout to the 

 adipose 1.0; snout to insertion of the pelvics 1.7; snout to the origin 

 of the anal 1.3; greatest depth 3.4. Proportions of the length of the 

 head: Diameter of eye 3.1; length of upper jaw 3.7; depth of caudal 

 peduncle 3.7; length of caudal peduncle 3.1. There are 37 segments 

 in the body. 



Remarks. — Several characters are remarkably changed during the 

 development of this species. The intestine coils and the anus moves 

 anteriorly nearer to the level of the origin of the ventrals. The bases 

 of the ventrals move forward nearer to the bases of the pectoral. 

 The growth downward of the abdominal cavity also makes the bases 

 of the ventrals appear to move higher on the body. The depth of 

 the body and the bulk of the head increase so considerably that the 

 general shape of the adult fish Uttle resembles that of the long sUm 

 postlarvae. The rays of the pectoral and the ventral, especially the 

 latter, become greatly elongate. The adipose is the last of the fins 

 to appear. 



This pecidiar species of fish appears to be somewhat related to the 

 species of the genus Opisthoproctus of the family Opisthoproctidae, 

 which are found in the eastern Atlantic (Vaillant, 1888; Zugmayer, 

 1911a and 1911b; and Roule and Angel, 1933); the western Atlantic 

 (Gregory, 1933); and the western Pacific in the South China Sea 

 (Trewavas, 1933). No fish remotely resembling the present species 

 has been described from the eastern Pacific. From the species of 

 Opisthoproctus this species differs strikingly in the presence of a 



