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Show 1890.] SEXUAL CHARACTERS OF ARNOGLOSSUS. 541 that this was true in every case without exception, and having traced the gradual development of the peculiar character in the males, I no longer had any doubt that the two forms belong to a single sexually dimorphic species. I will now describe the differences between the two forms in some detail. The largest specimens of the male, or lophotes form, are 20 cm. long including the tail. The first dorsal ray is not elongated, and its length is contained 4| times in the length of the head ; it is thin and flexible and arises from the right side of the head, not from the edge. The 2nd, 3rd, 4th, 5th, and 6th dorsal fin -rays are elongated, the order of magnitude being 4th, 3rd, 5th, 2nd, 6th ; the fourth ray in a specimen of the length just mentioned measured 3*2 cm. or five sixths of tbe length of the head. The rays of the left pelvic fin, excepting the first, are also elongated as compared with those of the female, the 4th being the longest. In the specimen mentioned it was 2 cm. long, or half the length of the head. The eyes in the male are slightly larger than those of the female, as the following measurements show (the total length given includes the tail; the eyes were measured along the longitudinal diameter):- Total length. Diameter of eye. 13-2 cm. 6-5 mm. Males { 17-4 cm. 8-75 mm. 18-4 cm. 10-0 mm. ( 13-7 cm. 7-0 mm. Females ....<! 17*6 cm. 8*5 mm. [18-7 cm. 9-25 mm. The length of the upper jaw measured from its anterior extremity to the posterior end of the maxilla on the upper side is slightly smaller in the male than in the female, as the following measurements show:- Total length. Length of upper jaw. ,, . f 19-1 cm. 11-25 mm. Males .... | lg.4 c m > 10.5 m m , f 18-7 cm. 12-0 mm. Females.... | 1 8.5 c m > 11-25 mm. Up to the length of 13-2 cm. the males do not show any elongation of the rays of the dorsal or pelvic fins, and therefore do not differ in this respect from the females. But in male specimens 14-7 cm. long the character is already well-marked, the longest dorsal ray in a specimen of this length being five sixths of the length of the head, as in a full-grown specimen. In the full-grown adult female the character so conspicuous in the male is slightly but distinctly developed, that is to say some of the anterior dorsal fin-rays are slightly elongated. The 2nd, 3rd, |