606 Bulletin 47, United States National Museum. 



forward on caudal peduncle, nearly meeting posterior rays of dorsal and 

 anal ; vent immediately in front of anal fin, far behind the dilated ab- 

 domen, its distance from end of caudal 3^ in total length ; anal similar to 

 dorsal ; ventrals about f length of maxillary, very slender, apparently 

 of 5 or 6 slender rays, inserted much nearer front of anal tlian head, their 

 distance from anal about half their distance from tip of snout. Black, the 

 mandible lighter, the base and terminal portion of barbel and the caudal 

 translucent. No evident phosphorescent spot on cheek ; 4 series of minute 

 phosphorescent dots on abdomen, the lateral series extending but a short 

 distance behind ventrals, the median series uniting to form a single row 

 behind these fins. Length 4 inches. Off the coast of Southern Cali- 

 fornia in 603 fathoms, (avrpov, cavern; rr6//a, mouth.) 



Idiacanllnts antrostomm, GILBERT, Proc. U. S. Nat. Mus., 1890, 54, Albatross Station 2980, in 603 

 fathoms, off southern California. (Type, No. 44286. Coll. Gilbert.) 



Order U. LYOPOMI. 



This group, which contains the single family of Halosauridw, is thus 

 defined by Gill : 



Scapular arch constituted by proscapula, posterotemporal and post- 

 temporal, the post-temporal discrete from side of cranium and impinging 

 on supraoccipital ; hypercoracoid and hypercoracoid lamellar ; a foramen 

 in upper margin of hypocoracoid; mesocoracoid absent; actinosts nor- 

 mal; cranium with the condyle confined to basioccipital. Opercular 

 apparatus characteristic, the preopercle entirely detached from the sus- 

 pensorium (rudimentary and connected only with the lower jaw) ; oper- 

 culum normally connected, subopercle enlarged and partly usurping the 

 usual position of the preopercle, in company with the suborbital chain 

 which is extended backward to the opercular margin; bones of jaws, 

 palatines, and pterygoid complete and normal ; anterior vertebrae sepa- 

 rate ; ventrals abnormal. (Lyopomi, Gill, American Naturalist, Novem- 

 ber, 1889, 1016.) (Aw, loose; 7rti/j.a, operculum.) 



Family LXXXVI. HALOSAURID^E. 



Body elongate, compressed anteriorly, tapering into a very long and 

 slender tail, which becomes compressed and narrowed into a sort of fila- 

 ment. Abdomen rounded. Scales rather small, cycloid, deciduous; sides 

 of head scaly ; lateral line present, running along the sides of the belly, 

 its scales in the known species enlarged, each in a pouch of black skin 

 with a luminous organ at its base. No barbels. Head subconical, 

 depressed anteriorly, the flattened snout projecting beyond the mouth. 

 Mouth inferior, horizontal, of moderate size, its anterior margin formed 

 by the premaxillaries, its lateral margin by the maxillaries, which are of 

 moderate width. Teeth small, in villiform bands, on the jaws, the rudi- 

 mentary palatines and pterygoids ; none on vomer and tongue. Eye rather 

 large. Facial bones with large, muciferous cavities. Opercular appara- 

 tus peculiar, the preopercle entirely detached from suspensorium, rudi- 

 mentary, and connected only with lower jaw ; opercle normally connected ; 



