232 THE VOYAGE OF H.M.S, CHALLENGER. 



Family Halosaueid^. 



Halosaurus, Johns. 



Body elongate, compressed, terminating in an exceedingly long tapering tail ; 

 abdomen rounded. Snout much projecting beyond the mouth, which is inferior, of 

 moderate width. Facial bones with large muciferous cavities ; a series of luminous 

 organs is generally developed in the course of the mucous canal system. Suboperculum 

 large ; prseoperculum rudimentary ; interoperculum membranous. Eye large. Teeth 

 in villiform bands in the jaws, on the rudimentary palatines, and pterygoids ; none on 

 the vomer. A band of hyoid teeth. Dorsal fin short, opposite to the space between 

 ventrals and vent. Ajial fin exceedingly long, occupying the entire length of the taU ; 

 no caudal fin. Lateral line running near to the lower profile, and composed of larger 

 scales which bear the luminous organs. Gill-membranes entirely separate, with numerous 

 branchiostegals. 



Of this family which hitherto was known from a single example only, four species 

 were discovered by the Challenger, showing that it is widely and abundantly repi'csented 

 in the deep sea. 



The foUowiug observations have been made on a specimen of Halosaurus macrochir. 



The oesophagus, the inside of which is longitudinally folded, passes into the short 

 pear-shaped stomach, which is caecal, rather thin walled, and beset with short villi in its 

 interior. The pyloric portion of the intestine is provided with a series of ten appendages 

 which are not longer than the stomach. The intestine is nearly straight but wide, its 

 mucous membrane being raised in numerous low annular folds which become distinct at 

 a short distance behind the last pyloric appendage. 



The liver embraces the lower part of the oesophagus ; it possesses only one lobe, that 

 on the left side, which does not extend so far backwards as the stomach. 



The air-bladder is nearly destroyed. It is simple, occupying the posterior half of the 

 abdominal cavity. A thick nacreous stratum intervenes between the thin inner and 

 outer membranes. At its anterior extremity it is suddenly contracted into a narrow 

 tapering tube, which ends in a thread-like ligament attached to the dorsal side of the 

 lower part of the oesophagus. An open communication between the oesophagus and the 

 air-bladder does not seem to exist. The tube is surrounded by a muscular ring at the 

 place where it enters the air-bladder, and a thick muscular fascicle starts from this ring 

 to each side of the body of the bladder, gradually losing itself on its surface. 



The ovaries are two bands extending forwards beyond the stomach. They are 



