FISHES-SCYLLIODONTIDAE—TRIAKIS SEMIFASCIATUS. 
363 
its anterior convexity and the margin of the snout. The teeth are small and numerous, some¬ 
what flattened, with a middle, sub conical, acute prong directed obliquely outwards, and gene¬ 
rally a smaller one on either side of their base. The eyes are of moderate development, pro¬ 
vided with a nictitating membrane, their longitudinal diameter entering a little over six times 
in the length of the head, as measured above, when compared to the total length. At a short 
distance behind the orbit, and on a level with it, may be observed a rather small spiracle. The 
branchial splits, five in number on either side, are vertically elongated, and diminishing gradu¬ 
ally in size backwards ; the fourth corresponds to the anterior margin of the pectoral fin, hence 
the fifth is situated above the same fin. 
The first dorsal fin is somewhat nearer the ventrals than the pectorals, and its anterior mar¬ 
gin nearer the second dorsal than the extremity of the snout. It is also higher than long ; its 
upper margin being emarginated, sub-crescentic, with the anterior lobe rounded off, while the 
posterior lobe is acute. The second dorsal has the same shape as the first; is somewhat smaller, 
and its anterior margin nearly equidistant between the base of the pectorals and the tip of the 
caudal fin. The first anal fin is situated opposite the posterior half of the base of the second 
dorsal; it is deeper than long, smaller than the second dorsal, of which it has the general shape. 
The second anal fin is much longer than deep, and contiguous to the inferior lobe of the caudal 
fin, from which it is partly separated by a mere split. The caudal fin is short and proportionally 
rather elevated and posteriorly truncated obliquely downwards and inwardly ; its lower lobe 
being quite small. The ventrals are short and broad, sub-triangular, slightly sub-concave 
posteriorly, and inserted nearer the extremity of the snout than the tip of the caudal. The 
pectorals are larger than the ventrals, short and very broad, sub-concave upon their posterior 
edge and rounded upon its angles, the outer one of which being rather prominent. 
The scales, or rather the shagreen, which covers densely all the outer surface, has the middle 
point more acute than in T. scyllium, giving it a more prickly appearance. The lateral points 
are very exiguous and oftentimes wanting. The keels, on the other hand, are quite con¬ 
spicuous. 
The ground color is olivaceous grey, lighter beneath than above, becoming yellowish under 
the head and throat. The upper surface of the head and the dorsal region exhibit transverse 
bands of deep black, with intervening small rounded spots of the same color along the middle 
line of the back, whilst other similar spots, varying in size, may be observed along the sides of 
the body and alternating with the bands just alluded to. A black spot exists also at the base 
and upper surface of ventrals and pectorals. The caudal fin itself, the second anal and dorsal, 
are entirely spotted, whilst the first dorsal and anal are unicolor, except the former, the base of 
which is affected by the transverse bands of the back. 
List of Specimens. 
Catal. 
No. 
No. of 
spec. 
Age. 
Locality. 
When col¬ 
lected. 
Whence obtained. 
Nature of 
specimens. 
Collected by— 
388 
i 
Presidio, California. 
1853 
Lt. W. P. Trowbridge . 
Alcoholic. 
Lieut. Trowbridge.... 
991 
i 
Young. 
Monterey, California.... 
1856 
A. S. Taylor, Esq. 
....do.... 
A. S. Taylor. 
