142 PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 



Chitonotus megacephalus. 



D. Ill, VII I 15-10. A. 15-16. C. 9 I 11 I 9. P. 18. V. I | 3. 



Body deepest under origin of first dorsal, thence decreasing regularly 

 to the caudal peduncle, which at its narrowest part is about two-sevenths 

 of the greatest depth. Hinder part of head almost quadrangular in sec- 

 tion, compressed, the compression increasing from the eyes forward. 



Head 3 rj-S^^ ; greatest depth 6f times in total length. Greatest 

 width at gill-covers slightly less than greatest depth. 



Eyes large, oval, about 3| times in length of side of head, their lon- 

 gitudinal diameter exceeding the length of the snout by about five- 

 twelfths ; the hinder margin of the orbit rather nearer the tip of the 

 operculum than that of the snout, and the interorbital space very nar- 

 row, so that the eyes are directed obliquely upwards. 



Upper jaw slightly longer than the lower, which is received within 

 it ; posterior extremity of maxillary slightly in front of or beneath the 

 posterior orbital margin. Teeth in both jaws villiform, sharp, uniform, 

 in a long but not wide band. Intermaxillaries protractile downwards. 

 Snout convex longitudinally and transversely. 



Nostrils with membranous tubes; the anterior lateral, in a line between 

 the centre of the eye and the tip of the upper jaw ; the posterior in a 

 concavity between the extremities of the ascending processes of the pre- 

 maxillaries and the raised anterior upper orbital margin. Nasal ten- 

 tacles long but narrow, situated above the anterior nostril and just in 

 front of the sharp, backward-directed nasal spine. Eye tentacles simi- 

 lar to nasal tentacle. 



Four preopercular spines ; the upper longest, with 2-4 prongs on its 

 upper side besides the tip ; second horizontal ; third directed down- 

 wards ; lowest directed downwards and forwards. 



Operculum unarmed, its membranous tip vertical with the first ray of 

 the second half of the first dorsal. An inner and outer pair of spines 

 behind each eye on top of head, outer spines the larger. Posterior to 

 these spines a short ridge, ending in a backward-directed spine on back 

 of head. Area between these spines somewhat concave transversely. 

 Suborbital ring and stay narrow. 



Origin of first dorsal over the commencement of the free horizontal 

 upi)er border of the operculum. First ray nearly equal in height to the 

 length of the head, second about two-thirds as long, third shorter than 

 fourth, a7id separated from it by an interspace twice as long as the others, 

 the membrane between these rays also deeply notched. Fifth and sixth 

 rays longer than the fourth or than the following rays, which gradually 

 diminish, giving the upijer margin of the second part of the spinous dor- 

 sal a rounded outline. Central rays of second dorsal about half as long 

 as the head. Anal similar to second dorsal. 



Pectoral fanlike, its base very oblique, parallel with the hinder mar- 

 gin of the operculum, its longest rays about equal to four-fifths of the 



