1898.] M'Intosh.— A^<?/^ on a Post- Larval Fierasfer. 63 



in ** a short stout spine, the point of which alone is uncovered 

 with the skin " (Couch)^ on the dorsal ridge in F. deyitatus. 



No larval or post-larval example of Fie7'asfer dentatus has 

 been described, for Prof Emery's example was 205 mm. in 

 length. The adult is distinguished by its dentition and the 

 presence of fin-rays in the caudal region. 



The specimen which has given origin to these remarks 

 was procured by Miss Delap, whose captures of rare marine 

 forms are familiar to many zoologists, at Valentia, on the 

 south-west coast of Ireland, and kindly forwarded for ex- 

 amination by Dr. Scharff, of the Science and Art Museum, 

 Dublin. It occurred in the tow-net in September, and measures 

 76 mm. in formaline. It was a post-larval form, though from 

 the peculiar whitish opacity of the abdomen it might be 

 imagined yolk was present. No teeth were yet developed in 

 the jaws, and therefore the species was in contrast with such 

 forms as Aphia, in which they are precocious. The head and 

 abdomen formed the deepest and widest part, the body being 

 nearly uniform in diameter for some distance behind, and then 

 tapering to a hair-like tail marked by pigment-dots both 

 dorsally and ventrally. The notochord appeared to cease at 

 the commencement of the most filamentous portion, which 

 had no fin-ra3^s. The development of the fin-rays of the 

 dorsal and anal fins is remarkable, the fish probably using 

 them more or less as levers in the body of its host, and in 

 going into the aperture tail foremost. The fin-rays form a 

 regular series of slender parallel rods which become fibrous 

 and flexible at the tip and spread out a little, the whole in- 

 vested by the cellular skin, and forming a continuous web. 

 The spine is opposite the point of the serrature of the fin. In 

 the adult F. acus the fin seems to be proportionately less 

 developed than in the post-larval stage, but the spine is 

 very tough, and is hollow at the base. The ossific tissue 

 forms an investment for the cellulo-granular contents. The 

 central cavity disappears towards the tip, which breaks up into 

 fibrillae. The rays in the ventral fin are longer than in the 

 dorsal, but in the latter the intermediate tissue is thicker at 

 the base — probably due to development of connective tissue. 

 Towards the tail the backward slope of the rays is greatly 

 increased, so that the terminal ones form a very small angle 

 with the notochord. 



I Fishes, vol. iii., p. 134' 



A 3 



