HALOSAURIDE. 295 
the species of the second group they are more opaque. It is likely this 
difference is due to the more advanced and perfect development of the 
lanterns accompanied by the greatly differentiated scales on the species of 
the second division. The type of Halosaurichthys Alc., 1889, was a species 
belonging to the subgenus Halosaurus ; the genus was based on insufficient 
or incorrectly interpreted characters, and has since, in 1896, been dropped 
by its founder. In their latest publications Goode and Bean and Collett 
retain Halosaurichthys and further divide the remainder of Halosaurus into 
two genera. Goode and Bean name their genera Halosaurus, Aldrovandia, 
and Halosaurichthys ; and Collett names his Halosaurus, Halosauropsis, and 
Halosaurichthys. Aldrovandia and Halosauropsis differ only in name. 
Goode and Bean characterize Aldrovandia thus: ‘* Lyopomi, with ventrals 
normal; no second dorsal fin; vertex scaleless; scales of the lateral line 
enlarged, provided with photophores. Head with pointed snout and promi- 
nent lateral ridges. Anal fin moderate, high; its height one third to one 
fourth that of dorsal. Type Halosaurus rostratus Giinther.” The others 
being possessed by all the family, the only features of those mentioned that 
serve for distinguishing characters among the species are the scales on the 
crown and the enlarged scales on the lateral line; but the existence of 
intermediate species. with very thin transparent scales on the crown and 
with scales on the lateral line moderately enlarged reduces the value of 
these characters in a diagnosis of either genus and makes it difficult to draw 
the line of generic separation. Collett says of his genus Halosauropsis that 
it is “ Semblable au genre Hualosaurus, mais les organes lumineux de la téte 
et de la ligne latérale sont recouverts d’une membrane en forme de sac 
souvrant en bas. Type: H. macrochir Gthr., 1878.” Probably the speci- 
mens of Halosaurus examined by this author, and with which he compared, 
had been injured, as the organs of the lateral system are similar in structure 
throughout the family; the lanterns of H. Owenw, and of others of the 
group in which these organs are less developed, are provided with the very 
thin, in cases hardly visible, membranous sac-like coverings opening down- 
ward. In their development the enlarged scales, which bear the fusiform 
luminous organs, have become superstructures by spreading over and cover- 
ing the regular scales in their own series at each side and in the adjoining 
series backward, thus compelling a decrease in the number of the glandular 
bodies as the seales increased in size. The species grouped under Aldro- 
vandia, or Halosauropsis, form the second of the subgenera mentioned above, 
