340 



U. S. p. R. R. EXP. AKD SURVEYS — ZOOLOGY — GENERAL REPORT. 



TETRAODON POLITUS, G r d . 



Smooth Balloon-Fish. 



Spec. Chab. — Body sub-cylindrical. Head very large, conslituting the third of the length, caudal fin excluded. Pectorals 

 broad, short, and rounded. Cauda! posteriorly sub-convex. Skin perfectly emootli all over, the prickles remaining within the 

 derm in the shape of indurated needles. Olivaceous brown above, maculated with black; yellowish and unicolor beneath. 



The head is sub-quadrangular, suh-pyramidal, larger across the tlioracic region than the 

 anterior portion of the body. Its upper surface is gently convex and quite declivous from the 

 eyes to the snout, which is obtusely rounded off. The lips are thick and fleshy, with their 

 surface papillar, the mouth being proportionally large. The eyes are rather small, sub-ellip- 

 tical, approximating the upper surface of the scull, their longitudinal diameter entering nearly 

 eight times in the length of the side of the head. 



The body from the thoracic belt tapers regularly backwards. The peduncle of the tail is com- 

 pressed, becoming quite thin at the insertion of the caudal. The height of the dorsal fin is 

 more than twice the length of its base ; its upper margin is sub-convex ; its origin is equidistant 

 between tlie branchial apertures and the posterior margin of the caudal fin. The anal is inserted 

 opposite the dorsal and somewhat further backwards ; it is narrower than the dorsal, and nearly 

 as deep as the latter is high, its inferior margin being quite convex. The caudal is posteriorly 

 sub-truncated ; else broadly rounded off, and contained short of six times in the total length. 

 The pectorals are very broadj rather short, posteriorly rounded off, or else convex. 



D 1, 7; Al, 6; C 2, 1, 4, 4, 2; V ; P 15. 



The skin is perfectly smooth to the touch. The small spines or prickles which are observed 

 in other species of this genus appear to remain in the present one in an undeveloped or 

 embryonic condition within the skin. 



The specimen described is somewhat over twelve inches in total length. 



The upper region of the body and head is olivaceous brown, maculated with black, minutely 

 and profusely dotted with black also ; the inferior region, from the middle of the flanks, being 

 uniform yellowish, sometimes merging into an orange tint. The dorsal and caudal fins are 

 olivaceous brown ; the pectorals and anal yellowish. 



List of specimens. 



