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[91] MATERIALS FOR A HISTORY OF THE SWORD-FISHES. 379 
furnished, besides, with a like series of vertically placed, conical, strong 
teeth of a comparatively uniform size, alternating with smaller, 1 to 3 
pair between each of the larger; small teeth cover, further, the greatest 
portion of the palatal region. The teeth in the under jaw are somewhat 
smaller, but more closely placed; instead of the outer principal series is 
seen a belt of smaller teeth. The gills show nothing different from the 
ordinary fish-gills, neitber have they yet the Xiphias character. 
Very young Sword-fish 37 miilimeters long, of which the head eonsti- 
tutes nearly the half (17 millimeters), have the lower jaw 34 millimeters 
Shorter than the upper jaw; in a somewhat larger example (50 milli- 
meters), the height of the dorsal and anal fins equals that of the body 
behind the head (3 millimeters); dark cross-bands descend over the 
sides of the body and the unpaired fins; the two small keels of the tail 
are of like form and size, with a median keel; the caudal is rounded. 
(Plate IT, Fig. 10). In this small fish, in other respects, the armament of 
the skin and the jaws is essentially as in the above-described young 
Sword-fish four to five times as large; the larger pointed skin-plates are 
also here perceptible as such, likewise their above-described regular 
arrangement. The lateral margin of the forehead is toothed; the pre- 
operculum, likewise, in the smaller of these two examples is even furnished 
with a group of long spines, which in the space of this treatise will be 
described in various other Scombroids. In still younger examples the 
larger skin-plates diminish in namber, and each plate bears only two or 
three small points of equal size; there is here as little trace of ventrals 
as in the very youngest developmental stage (10 millimeters). The 
head, which constitutes nearly half of the total length, though the bill 
is still short, is here compressed, without the frontal depression of the 
Histiophori, and extends out into a comparatively short bill, broad at the 
root, the under jaw of which is just as long as the upper jaw, both being 
well provided with teeth. The frontal margins are serrate just as in the 
above-described larger young; likewise the opercular spines; the larger 
nuchal spine and the preopercular spine, which are so colossal even in 
the youngest Histiophort, are wanting. On the contrary the pointed 
skin-covering is already perceived like fine bristles which project from 
the skin; in the nuchal region, over each gill-opening, oceurs a little 
projecting pointed crest. 
Despite certain analogies between Xiphias and Histiophorus at their 
appearance from the egg, there are very considerable differences between. 
them in their very first conduect—differences which show well enough 
that the separation between these two genera is rather wide. To this 
result one must come also by comparison of the bony structure of a 
Histiophorus or a Tetrapturus with that of a Xiphias. The closest ge- 
neri¢ ally of the Histophori, especially of the Terapturi, we will, in a 
later section, find in the genus Acanthocybium, which presents decided 
resemblances. If these show tothing’ more than a very close relation- 
ship, they at any rate unite the tie too firmly for one to regard the 
Xiphioids as other than a subsection of the great mackerel family. 
