OCR Text |
Show 324 MR. R. COLLETT ON CERTAIN GOBIOID FISHES. [Mar. 5, kind, few in number, but long and cylindrical. The posterior rays of the anal and second dorsal fins are, as a rule, not shorter than the anterior, making the fins about even in their whole length. The caudal fin is slightly square, with rounded edges in the young individuals, but truncated in the elder ones. The nearly mature females, not yet quite ready for spawning, agree in general with the individuals in the immature state, from which they differ in the somewhat swollen belly. The females ready for spawning have an average length of about 42 millims.; many having the spawn ripe are of a length of 38 millims.; none reach a length of more than 46 millims. (the caudal included). The head is not visibly thickened, but is about the same as during the whole young period ; it is rather more pointed than in the male; the cleft of the mouth is considerably smaller, although the jaws may possibly have become a trifle longer than before. The teeth, however, have not undergone any change, but are uniform, exceedingly fine, and placed in the same row as in the young individuals. The caudal fin is emarginated, and the anal and the second dorsal are tapering behind, as is the case in their younger state. The construction of the body is slender and elongated, laterally compressed ; and it is only during the spawning-season that the body of the male becomes thicker and more plump. A specimen of medium size out of the spawning-season has a total length of 40 millims., of which the head is 9 millims. ; and this is contained about 4*4 in the total length (the caudal fin included). The greatest height is 5*5 millims., or contained 7*2 in the total. The vent is situated about 2 orbital diameters nearer the snout than the root of the caudal. In the spawning-season the body becomes fully developed, although the total length does not increase. In a male with a total length of 40 millims. the length of the head is 9*5 millims. (4*2 in the total) ; in the female about the same as before. The eyes have a diameter of 2 millims., and occupy |- of the length of the head. The orbital space, which, as a rule, is narrow, and does not reach the breadth of an orbital diameter, has in the mature male fully the last-named breadth. The number of the gill-rays is 5 ; the gill-openings are wide, and stretch forwards to about the middle of the orbit. The mouth is oblique, and the lower jaw longer than the upper, the maxillary extending to below the middle of the orbit. During the spawning-season the jaws of the male become considerably larger and more oblique ; at the same time, the head and all parts of the body become swollen, the jaws extending much deeper under the eye. The number of the vertebrae is 27 ; the processus spinosi are very long, and reach almost to the dorsal and ventral line. The medulla spinalis extends as far hack as to the middle of the 22nd vertebra. The teeth.-Before the spawning-season the structure of the teeth is exactly alike in both sexes. In each of the jaws is found on both sides a single series of 20-25 minute and very closely fitted |