18. OPISTHOGNATHUS. 265 



length, the length of the head 3| ; the distance between the eyes is 

 one-half of their diameter. Yellowish, marbled with bro\vn ; max- 

 iUaries -n-ith a black inferior mai'gin. A black ovate spot between 

 the fourth and eighth dorsal rays. 

 Red Sea ; coast of Pondicherry. 



2. Opisthognathus megastoma. 



D. 27. A. 18. 



The upper maxillary is very long, and reaches to, or slightly beyond, 

 the base of the pectoral fin. Scales exceedingly small. The height of 

 the body is one-fifth of the total length, the length of the head one- 

 third. The distance between the eyes is one-fifth of tlieii- diameter. 

 An ovate black spot between the seventh and tenth dorsal rays. 



Gulf of Mexico. 



a. Adult. Gulf of Mexico. From the Haslar Collection. 

 h. Adult, Gulf of Mexico. From the Haslar Collection. 



Description. — This species is very closely allied to 0. nigromargi- 

 natus, from which, however, it may be readily distinguished by the 

 characters in the diagnosis. The greatest depth of the body is below 

 the origin of the dorsal, where it is contained five times in the total. 

 The head is very large and thick, its length being one-third of the 

 total. The occiput and the nape of the neck are broad, the space 

 between the eyes very narrow, and the snout short and obtuse. The 

 cleft of the mouth is slightly oblique and exceedingly wide, its angle 

 being placed behind the posterior margin of the orbit. The inter- 

 maxillary is elongate, and reaches as far backwards as the cleft of 

 the mouth. The maxillaiy is prolonged into a dilated, flexible, 

 sabre-shaped ai)pendage, which extends to, or sHghtly beyond, the 

 base of the ventral ; its upper margin is fixed to the mandibula by a 

 wide membrane, which has a large ovate opening. An additional 

 and moveable bone, attached to the maxillaiy, supports the mem- 

 brane above the opening. The eye is veiy large, 3| in the length 

 of the head, and sHghtly directed upwards. The nostrils are smaU, 

 without appendage. The margin of the prceoperculum is rounded, 

 and partly covered by the overlapping maxillary. A rather feeble 

 opercular spine is hidden by the skin, and the extremity of the sub- 

 operculum extends beyond this spine. The giU-opening is wide, but 

 does not extend on the upper side of the praeoperculum ; the branchial 

 membranes of both sides are slightly joined on the thi-oat. 



The dorsal fiji begins above the extremity of the operculum, and 

 is of nearly equal height in aU its length. The unarticulated rays 

 pass insensibly into the articulated ones ; all are flexible. The di- 

 stance between the dorsal and caudal fins is equal to the height of 

 the tail below the end of the dorsal. The caudal is slightly rounded, 

 one-seventh of the total length. The origin of the anal falls ver- 

 tically below the twelfth dorsal ray, and its end opposite to that of 

 the dorsal ; it equals that fin in height. The pectoral is short, 

 rounded, about one-eighth of the total length, and does not extend 



