FISHES OF HAWAIIAN ISLANDS. 
33 
with the cavity of the abdomen; gill-slits in great number, the water being expelled through an 
abdominal pore in front of the vent; jaws none, the mouth a longitudinal fissure with cirri on each 
side; body lanceolate in form, more or less fish-like, and not enveloped in a tunic; dorsal fin present, 
low; analfin usually more or less developed. 
Small marine animals, highly interesting to the zoologist as exhibiting the lowest degree of devel- 
opment of the vertebrate type. The class includes but the single order, Arnphioxi or Oirrostomi. 
Order A. AMPHIOXI. The Cirrostomes. 
This order is equivalent to the family Branchiostornidx. 
Family I. BRANCHIOSTOMI DT. — The Lancelets. 
Body elongate, lanceolate, compressed, naked, colorless; fins represented by a low fold extending 
along back, with usually a rudimentary fold below, which passes by the vent to the abdominal pore; 
mouth inferior, appearing as a longitudinal fissure, surrounded by conspicuous, rather stiff cirri; eye 
rudimentary; liver reduced to a blind sac of the simple intestine. 
Small, translucent creatures, found embedded in sand on warm coasts throughout the world. 
Eight species are now recognized, referable to two or three genera, all very similar in appearance and 
habits. Only one genus represented in the Hawaiian fauna. 
Genus I. AMPHIOXIDES Gill 
“ Branchiostomids with bilateral (?) gonads, no rayed sympodium (?), low dorsal fin, expanded 
caudal membranes, and oral cirri aborted (?).” (Gill.) 
As the species on which this genus is based really lacks oral tentacles, it should stand as a distinct 
genus. To say that this trait is due to its pelagic habit, as Tattersall suggests, is not to discredit its 
generic value. 
Amphioxides Gill, Genera of Branchiostomidse, Am. Nat., vol. xxix, May, 1895, 458 ( pelagicum ). 
1. Amphioxides pelagicus (Gunther). Fig. 1. 
Buccal tentacles absent; 0 gonads not fully developed, extending from the first to the twenty-sixth 
myocomma and forming 2 series in the middle; atrial cavity extending somewhat behind the sup- 
posed position of the atrial pore; anterior end of the notochord enveloped in a very strong sheath; 
the posterior (J mm.) not covered by the myocommas, which lean off abruptly, and extending right 
to the hind margin of the caudal fin; eye distinct; nerve-cord with minute pigment-spot .( arranged 
intracentrally with regard to the myocommas; dorsal fin-rays low, but very distinct, about five to 
each myocomma; dorsal fin-fringe becoming distinct about the twenty-seventh myocomma, gradually 
becoming somewhat higher behind, its rise more abrupt where it passes into the caudal fin, which is 
paddle-shaped and bilaterally symmetrical with regard to the notochord; lower half of caudal passing 
uninterruptedly into the ventral, in which no rays are developed, this fin seeming to be continued 
forward as a low fringe for some distance beyond the supposed position of the atrial pore; nearly the 
whole of this fringe showing a minute vertical striation, especially in- its higher portions; myocommas 
27, of which 15 belong to the tail; how many should be attributed to the portion between vent and 
atrial pore is uncertain on account of the difficulty in ascertaining the position of the latter. This 
pore could not be made out, and its position is supposed to be opposite to the thirty-sixth myocomma 
only from analogy or comparison with other species, and from a slight contraction of the muscular 
layer at this point. 
a This can not be due to the age of the individual, as they are clearly developed in specimens of Branchiostoma bel- 
cheri (?) of only half the size of this specimen. 
F. C. B. 1903—3 
