ATHERINA LACU8TRIS. 67 



Atherina lacustris (BONAPARTE). 



1 D. 59, 2 D. 1/10 13, A. 1/1215. Scales: lat. line 4660, 



trans. 1011. 



This is a small species, with an elongated body, eight times as long as 

 high, and one and a half times as high as thick. The dorsal contour is 

 nearly horizontal, except towards the head, where it becomes convex. The 

 abdominal outline is similar, but rather more curved, so that the tail is 

 attenuated. 



The head is one-fifth of the total length. Its upper surface is flat. A 

 median longitudinal ridge extends between the eyes, and is prolonged forward, 

 as are the lateral ridges from the superciliary region. The eye is two-fifths 

 the length of the head. The inter-orbital space, which is equal to the length of 

 the snout, is two-thirds of the orbital diameter in width. The cleft of the 

 mouth is directed obliquely downward. The maxillary bone extends below the 

 front margin of the eye. There is a simple row of small pointed teeth on the 

 pre-maxillary bone, and on the mandible ; they are longest in front. There 

 are no teeth on the vomer or palate. The gill-aperture is large. The gill- 

 rakers are small and tooth-like. The pre-operculum forms a right angle, with 

 the angle rounded. The head is covered with scales as far forward as the eyes. 



Von Martens counted the rays in the dorsal and anal fins in sixty speci- 

 mens, with the result that they exhibited twenty-three variations in the fin 

 formula. Nearly two-thirds had seven rays in the first dorsal, three-fourths 

 had twelve rays in the second dorsal, while in the anal fin nearly half had 

 thirteen rays, and in more than a third there were twelve rays. There is no 

 relation between the size of the fish and the number of fin-rays. 



The pectoral fin is pointed; it is four-fifths of the length of the head. 

 The ventral fins are rather shorter, and their insertion is in front of the ex- 

 tremity of the pectoral fin when laid back. The small first dorsal fin is two 

 or three scales farther back than the base of the ventral ; it is the length of 



* O 



the head behind the operculum, and a like distance separates it from the second 

 dorsal fin. The base of the anal fin is a little in advance of the base of the 

 second dorsal ; the fin is rather larger than the second dorsal. In both fins 

 the second ray is twice as long as the first ; the rays diminish in length 

 rapidly; none of them are branched. In both fins the posterior border is con- 

 cave. The caudal fin is deeply forked, and the rays are subdivided. 



The lateral line is nearly horizontal. It usually contains sixty scales ; but 

 Von Martens records instances in which the number is only forty-five. They 

 are silvery and deciduous, like the other scales in the longitudinal lateral 



