138 



The Grayling and the Smelt 



numerous specimens of this species were found dead, floating 

 on the water, by the steamer Albatross. 



The Idiacanthida are small deep-sea fishes, eel-shaped and 

 without pectorals, related to the Iniomi. 



Order Lyopomi. Other deep-sea fishes constitute the order 

 or suborder Lyopomi (Xvos, loose; ncapa, opercle). These are 

 elongate fishes having no mesocoracoid, and the preopercle 

 rudimentary and connected only with the lower jaw, the large 



FIG. 100. Aldrovandia gracilis (Goode & Bean). Guadaloupe Island, West 

 Indies. Family Halosauridte. 



subopercle usurping its place. The group, which is perhaps to 

 be regarded as a degenerate type of Isospondyli, contains the 

 single family of Halosaurida, with several species, black in 

 color, soft in substance, with small teeth and long tapering 

 tail, found in all seas. The principal genera are Halosaurus 

 and Aldrovandia (Halosauropsis). Aldrovandia macrochira is 

 the commonest species on our Atlantic coast. 



Several fossil Halosauridce are described from the Creta- 

 ceous of Europe and Syria, referred to the genera Echidnocephalus 

 and Enchelurus. Boulenger refers the Lyopomi to the suborder 

 Heteromi. 



