334 MR. R. COLLETT ON CERTAIN GOBIOID FISHES. [Mar. 5, 



The eyes are situated perfectly laterally, so that the lower margins 

 do not seem to project more than the upper. The interorbital space 

 is, in the female and young specimens, not broader than 'the diameter 

 of the eye, in the full-grown male a little larger. The branchio- 

 stegals are 7 in number ; the gill-openings are wide. 



The mouth is oblique, with the lower jaw the longer. In the 

 female and the young males the lower jaw is almost straight, or 

 only faintly bent, and the intermaxillary bones are quite even in 

 their outer margin ; but in the full-grown male the jaws receive a 

 special development during the spawning-season. The inter- 

 maxillary bones then become broad, and form on each side of their 

 margin a distinct projection, almost in the form of a nail ; at 

 the same time that the teeth reach their full development the 

 lower jaw becomes long and strongly curved upwards, and when the 

 mouth is shut it reaches a little in front of the intermaxillary bones, 

 the projecting nail of which encloses the almost angularly curved 

 upper part of the lower jaw. The point of the latter jaw is square, 

 and, as is the case with the intermaxillary bones, in the male den- 

 tiferous. In these old males the gape reaches backwards to the 

 posterior margin of the eye, whilst in the female and the young 

 males it scarcely reaches beyond the middle of the eye. The length 

 of the lower jaw in proportion to the total length is in the old males 

 as l:7f, in the female as 1:10|. 



The number of vertebrae is 29. 



The teeth. — Whilst during its immature state Latr. pellucidus has 

 a construction of the teeth common to both sexes, which continues 

 permanent in the female, whilst the male towards the spawning- 

 season in a comparatively short time changes these teeth for another 

 set of a totally different construction, this is not the case with 

 Crystallogobius nilssonii. First, the female is perfectly toothless 

 all her life ; secondly, the teeth of the male, which are com- 

 posed of both small and acute teeth and long canine teeth, are 

 developed very early, and all reach their full size during the spawning- 

 season. 



The exact time when the teeth make their appearance in the young 

 is probably when they are about two months old. A young one, 

 with a total length of 21 millims., and perhaps about one month and 

 a half old, had no traces of teeth. 



In the young males, which have reached a total length of 26-28 

 millims., the teeth begin to show themselves in the intermaxillary 

 bones and the point of the lower jaw ; at this period all the teeth 

 are about equal in size. 



In the male during the spawning-season, when the teeth have 

 reached their full size, the projecting intermaxillary bones have on 

 their upper and prominent portion a single row of closely placed, 

 small, acute, and curved teeth, 13-14 in number, on each side 

 (see fig. 4) ; on the lower square margin one or two teeth directed 

 straight downwards or backwards are found. The maxillary bones 

 are without teeth, as well as the vomer. In old males the outer 

 part of the lower jaw runs out in a long upward curve, which at 



