The Apodes, or Eel-like Fishes 157 



it is possible that all three are really the same species, for which 

 the oldest name would be Saccopharynx ampullaceus. Of this 

 form four specimens have been taken in the Atlantic, one of 

 them six feet long, carried to the surface through having 

 swallowed fishes too large to be controlled. To be carried above 

 its depth in a struggle with its prey is one of the greatest dangers 

 to which the abysmal fishes are subject. 



Order Heteromi. The order of Heteromi (erepos, different; 

 a? ywob, shoulder), or spiny eels, may be here noticed for want of 

 a better place, as its affinities are very uncertain. Some writers 

 have regarded it as allied to the eels ; some have placed it among 

 the Ganoids. Others have found affinities with the stickle- 

 backs, and still others with the singular fresh-water fishes called 

 Mastacembelus. The Heteromi agree with the eels, as well as 

 with Mastacembelus, in having the scapular arch separate from 

 the cranium. Unlike all the true eels, most of the species have 

 true dorsal and anal spines, as in the Percesoces and Hemi- 

 branchii. The ventral fins, when present, are abdominal and 

 each with several spines in front, a character not found among 

 the Acanthopteri. There is no mesocoracoid. 



The air-bladder has a duct, and the coracoids, much as in 

 the Xenomi, are reduced to a single lamellar imperf orate plate. 

 The two groups have little else in common, however, and this 

 trait is possibly primitive in both cases, more likely to have 

 arisen through independent degeneration. The separation of 

 the shoulder-girdle doubtless indicates no affinity with the eels, 

 as the bones of the jaws are quite normal. Two families are 

 known, both from the deep sea, besides an extinct family in 

 which spines are not developed. 



The N otacanthidcE are elongate, compressed, ending in a band- 

 shaped, tapering tail; the back has numerous free spines and 

 few or no soft rays, and the mouth is normal, provided with 

 teeth. The species of Notacanthus are few and scantily pre- 

 served. Those of Macdonaldia are more abundant. Mac- 

 donaldia challengeri is from the North Pacific, being once taken 

 off Tokio. The extinct family of Protonotacanthidcz differs in 

 the total absence of dorsal spines and fin-rays ; the single species, 

 Pronotocanthus sahel-alma, originally described as a primitive 

 eel, occurs in the Cretaceous of Mount Lebanon. 



