TRACHYPTERIDiE. 
321 
Lutken has specified certain osteological distinctions 
between the genera Regalecus and Trachypterus, chiefly 
affecting the general structure of the skeleton. In Rega- 
lecus, which is usually of considerably greater dimen- 
sions, in spite of this the skeleton is much looser, a 
circumstance which is, however, consistent with the fact 
that Regalecus is a deep-sea genus of a still more marked 
description. As we have seen above, there is no lack of 
characters to distinguish between the two genera; but on 
the other hand, it cannot be denied that they are very 
closely related to each other, especially if the changes 
of development be taken into consideration. 
The earliest stages have hitherto been almost unknown; but by 
the kindness of Professor Leche we are here enabled to give some 
damaged and indistinct. The depth of the body, which is consider- 
ably less than the length of the head, gradually decreases from the 
occiput to the very end of the tail, which is furnished with a long, 
though damaged and broken, caudal fin. This fin (fig. 86) consists 
of seven simple and unarticulated rays, the four lower ones articulating 
with the hypural bones, which are directed straight backwards, and 
the three upper with the end of the urostyle. The second and third 
rays from the top, however, are rudimentary, and the fin is thus di- 
vided into two parts, with one ray at the top entirely separated, to 
all appearance, from the lowest four rays by the interval referred to. 
All the rays are broken, but the pieces of the middle ray are still 
united by a thin filament, and end in an extremely fine filiform tip. 
This ray, as well as the uppermost and lowest rays, is also rough 
at the sides with two rows of spines pointing in opposite directions, 
a character which reminds us of the preceding genus. When perfect, 
this ray seems to have been half as long again as the head. An 
essential distinction between this genus and Trachypterus may thus 
be drawn from the circumstance that in the former the rudimentary 
details with regard to a specimen of Regalecus gladius , 36 cm. long, 
which he received at Messina. 
The head is perfect in the essentia] points, and shows that ex- 
tensive elongation of the preoperculum, the interoperculum and the 
hyomandibular, together with the quadrate bone, downwards and for- 
wards to a point in front of the perpendicular from the anterior 
margin of the eye by a distance equal to the longitudinal diameter 
of the eyey~ which sets the articulation of the lower jaw in such 
a position that the lower margin of the latter is perpendicular, when 
the mouth is closed, and thus forms the front of the head. The 
jaw-teeth are wanting. The operculum is triangular, with the hind 
corner, which forms the end of the head, obtusely rounded. Beneath its 
inferior side lies the suboperculum, which is of fairly uniform breadth, 
but somewhat broader behind than in front. Only the anterior part 
of the occipital fin is persistent, i. e. the first, strongest ray and the 
next four. The tips of these rays are broken off short, but their 
length is still about 1 / 3 greater than that of the head. Of the rays 
behind these there is no trace, in front of the dorsal fin proper, which 
begins in a line with the middle of the operculum. Each of the 
ventral fins contains only one ray, even this being broken, but in the 
left fin about equal in length to the head. The pectoral fins are 
rays are situated at the top of the caudal fin, in the latter at the 
bottom. In this circumstance we may perhaps find a partial expla- 
nation of the more general retention of the caudal fin in Trachypterus 
and its almost invariable loss in Regalecus. The other differences, 
however, affect only the degree and not the direction of the deve- 
lopment. 
We thus retain the genus Regalecus, but only as 
the expression of an intermediate stage between Lo- 
photes and Trachypterus. 
It is perhaps a matter of doubt whether more 
than one species is known from the Atlantic, the Medi- 
terranean, the East Indies" and Australia; but it is 
apparently certain that only one species of this genus 
belongs to the north of the Atlantic and the Scandi- 
navian fauna, that same species which on many, if not 
all, occasions has given rise to the mysterious accounts 
of the “great sea-serpent”. 
a It seems hardly probable that Regalecus Russellii from Vizagapatam is a distinct species. It has never reappeared since 1788, and 
there is no specimen of it in existence. Even Siiaw ( Gen . Zool., vol. IV, p. 195, tab. 28) regarded Russell’s Gymnetrus as an early stage 
of the development of Regalecus glesne. 
Scandinavian Fishes. 
41 
