FISHERY BULLETIN: VOL. 72. NO. 2 



were dissected. Drawings were made with the aid 

 of a projector and camera lucida. All the holotypes 

 are presently housed in the Marine Vertebrates 

 Collection of the Scripps Institution of Ocean- 

 ography. 



Names: The new species of the genus Mo/zo^na- 

 thus are named for John D. Isaacs of the Scripps 

 Institution of Oceanography (SIO), La Jolla; 

 Elbert H. Ahlstrom of the Southwest Fisheries 

 Center, National Marine Fisheries Service, La 

 Jolla; and Jesse N. Raju, wife of the author (noun 

 in apposition). 



KEY TO THE SPECIES OF 

 THE GENUS MONOGNATHUS 



la. Pectoral fin present 2 



lb. Pectoral fin absent 3 



2a. Head large, about 13.3 in total 



length, caudal fin normal M. isaacsi 



2b. Head small, about 9 in total 



length, caudal fin lanceolate M.jesse 



3a. Caudal fin normal, vertebrae long 4 



3b. Caudal fin either whiplike or 



paddle shaped, vertebrae short 5 



4a. Vertebrae 94, teeth in mandible 8, 



adipose region of dorsal fin with 



48-63 rays M.jesperseni 



4b. Vertebrae 88, teeth in mandible 12, 



adipose region of dorsal fin with 



36-48 rays M. hruuni 



5a. Caudal fin whiplike, dorsal 



commences on myotome 3, two 



ethmoid teeth M. taningi 



5b. Caudal fin compressed, paddle 



shaped, dorsal commences on 



myotome 13, one median ethmoid 



tooth M. ahlstromi 



MONOGNATHUS ISAACSI SP. N. 



Figures ID, I; 20 



Holotype: SIO 69-353, western North Pacific, 

 32^02. 3'N-32'=07.9'N, 156^07. 0'E- 156^06. 7'E, 

 depth of capture 0-950 m, IKMT, 1(56 mm), 

 2 June 1969. 



Description: Body elongate, compressed except 

 at head. Trunk clearly marked from tail, 2.9 

 in total length. Maximum depth at middle of 



body, 10.3 in total length. Head large, 7.6 in 

 total length. Snout moderately long, 2.4 in head. 

 Olfactory organ rudimentary, a short curved 

 tube open at both ends. Eyes tubular, small, 

 18.7 in head. Upper jaw soft, maxilla not 

 recognizable, no upper teeth. Skin inside of 

 mouth dusted with melanophores. Median eth- 

 moid tooth projects below level of lips, visible 

 from side. Lower jaw slightly longer than upper 

 jaw, with four small teeth. Mouth large, gape 

 reaching far behind eye. Postorbital distance 1.7 

 in head. No branchiostegals recognizable. Gill 

 opening small, ventrolateral. About 75 myotomes 

 could be counted and another 25-30 are estimated 

 for a total of about 100. Tail blunt at tip. 

 Stomach bulging, extending beyond trunk as a 

 sac. Dorsal fin high, originating behind gill open- 

 ings, with 80 unsegmented rays. Predorsal dis- 

 tance 3.7 in total length. Anal fin high, originat- 

 ing behind vent, with 52 unsegmented rays. 

 Preanal distance 1.5 in total length. Pectoral 

 fins small, rays not distinct. 



Pigmentation: Uniformly dark brown. 



Remarks: This is the first known specimen of 

 the Monognathidae with complete body pigmenta- 

 tion. The absence of an upper jaw and the 

 presence of an ethmoid fang indicate that M. 

 isaacsi is properly referable to the Monogna- 

 thidae. Of all the members of the Saccopharyngi- 

 formes so far known, this species represents the 

 most generalized form except for the reduced 

 eye, presence of the enlarged ethmoid fang, and 

 absence of the upper jaw. The shape of the body, 

 the head with its long snout and large mouth, 

 the nature of the median fins, and the presence of 

 pectoral and absence of ventral fins are typical 

 of eels. In Eurypharynx and Saccopharynx the 

 mouth is enlarged and the suspensorium highly 

 modified, and in Saccopharynx the tail is whip- 

 like. The snout in these genera is reduced whereas 

 it is long in M. isaacsi. 



The meristic and morphometric characters of 

 the three species described by Bertin (1938) and 

 the three new species described in this account 

 are given in Table 1. The relative lengths of the 

 head, cranium, snout, and predorsal distance are 

 the highest in M. isaacsi. The head is depressed. 

 The teeth in the lower jaw are different in shape 

 and fewer in number than in other species. The 

 median ethmoid tooth is long and projects into 



548 



