EKGASILTJS NANUS. 35 



but obvious constriction occurs near its middle. The 

 remaining thoracic and the abdominal segments small. 



Antennules short, apparently only five-jointed, and 

 sparingly setiferons ; the first joint about twice the 

 length of the second, the fourth rather smaller than any 

 of the others. Antennae tolerably slender and greatly 

 elongated, composed of three joints, and furnished with 

 moderately strong and curved terminal claws. Mouth- 

 appendages apparently more or less rudimentary or 

 obsolete. 



The first four pairs of thoracic legs all biramose and 

 well developed ; the first three pairs with both the 

 inner and outer rami three-jointed, but in the fourth 

 pair while the inner ramus is three-, the outer is only 

 two-jointed, the first joint being about twice as long 

 as the end one. The fifth pair small, and consisting 

 each of a single one-jointed branch which is about 

 three times longer than broad, with the lateral margins 

 subparallel, and the distal end truncated and bearing 

 two or three moderately long apical seta?-. Caudal 

 rami short. Egg-strings two, large, more than halt 

 the length of the animal and containing numerous 

 ova. Length, exclusive of egg-strings, 12 mm. 



Habitat. — Parasitic on the gills of the grey mullet, 

 Mugil chelo (Guvier). Bay of Nigg, Aberdeen, in July, 

 1900 (T. Scott). Swan Pool, Falmouth (A. M. Norman. 

 1884). 



This appears to be a rare species ; though we have ex- 

 amined several specimens of the grey mullet, we have only 

 once observed it. Another species, E. sieboldii, found parasitic 

 on carp, pike, and some other fresh-water fishes, appears to 

 have a wide distribution on the Continent and may yet be 

 obtained in British waters. 



We have not seen the male of Ergasilus nanus, nor have we 

 seen any published record of its occurrence; the male of E. 

 sieboldii, on the other hand, appears to be the form which 

 has been most frequently met with. Though several other 

 species of Ergasilus are recorded, E. nanus is apparently the 

 only British representative of the genus. 



