376 The Apodes, or Eel-like Fishes 
m2) 
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 (érepos, different; 
os, 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 Heteromit 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 Acanthoptert. There is no mesocoracoid. 
The air-bladder has a duct, and the coracoids, much as in 
the Xenomi, are reduced to a single lamellar imperforate 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 Notacanthide 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 Protonotacanthide differs in 
the total absence of dorsal spines and fin-rays; the single species, 
Pronotocanthus sahel-alme, originally described as a primitive 
eel, occurs in the Cretaceous of Mount Lebanon. 
