HALOSAURUS ATTENUATUS. 297 
caudal region. Greatest depth one sixteenth of the entire length. Head 
elongate, one eighth of the total length, retaining a considerable width for- 
ward but losing indepth. Snout more than half as wide as the head, preoral 
portion equal to half the length from the eye, broad, rounded and shovel- 
shaped at the end. Rostral cartilage with three longitudinal ridges below, 
bearing a series of prominences across the under side of the middle, blunt 
angled and rather wide at the end. Mouth medium, about twice as wide as 
long; maxillary extending little below the eye, with a sharp spine on its 
upper angle at the end. Teeth small, in villiform bands, similar to those of 
HH. radiatus but more slender, on jaws, palatines, and pterygoids. Eye 
medium, length more than twice the width of the interorbital space, more 
than five and one half times in the length of the head, two and one half 
times in the length of the snout. Nostrils small, close together, close to the 
orbit, anterior with a hood-like valve opening forward. Opercles thin, 
flexible, rather short, the muciparous canals extending farther back and end- 
ing in a couple of angles below the base of the pectoral. The opercle itself 
is dark colored and, apparently, the whitish membranes of the canals are 
applied to its surface. Gill arches rather short; eleven rakers on the first 
arch, shorter than the lamine, tubercular. Gill membranes hardly united, 
free from the narrow isthmus; gill lamin short, two fifths as long as the 
eye. Mucous canals greatly developed along the side of the head and below 
each lower jaw; that from the snout below the eye to the opercle is met by 
that from the chin below the pupil, both widening as they pass backward 
until at the end their width equals the length of the orbit. On the top of 
the head the development of the mucous system is hardly greater than on 
the flank. From the upper angle of the gill opening the lateral line system 
drops into and through the axil, below the base of the pectoral, until low 
on the flank where it passes backward, traced by an opaque whitish band 
‘(the nerve) under a series of scales upon which there is a series of vertical 
organs, probably light producers, which externally are covered by a thin 
transparent membrane. The vertical organs resemble those of Lampro- 
grammus, Plate XXXIV. fig. 5. 
Dorsal origin little more than two lengths of the head from the snout ; 
base twice as long as the eye, the same distance backward of the insertions 
of the ventrals; fin shaped like that of HZ. macrochir, higher than long, rays 
decreasing rapidly in Jeneth from the second backward; first ray shorter 
than the second, slender. Origin of the anal about three lengths of the 
