4 ARKIV FÖR ZOOLOGI. BAND 14. N:0 10. 



far reported as larger than the present one is A. scutiformis 

 Thiele, taken from the outside surface of Tetraodon and 

 Haliotus at Hakodate, Japan. 



In that species the cephalic area is relatively much Jar- 

 ger, the posterior lobes of the carapace are very much shor- 

 ter, the posterior sinuses of both carapace and abdomen are 

 shorter and the supporting ribs of the sucking disks differ 

 greatly in structure. 



Achtheiniis japonicus New Species. Pl. 2, figs. 9—17. 



Höst and record of specimens. Four adult females and 

 three younger ones but little beyond the chalimus stage 

 were taken from the fin of Acanthias sp. at Misaki, Japan, 

 May, 5, 1914. The adults become the types of the new 

 species. 



Unlike some of the other species of the genus they do 

 not dig into the skin when attaching themselves. They 

 simply insert the tips of the second antennae and the ter- 

 minal claws of the maxillipeds, and hold on also with the 

 pads on the latter appendages. In consequence they are 

 more easily detached from their höst than is usual in the 

 genus. 



Specific characters of female. General body form elon- 

 gate, about twice as long as wide, and rather squareJy trun- 

 cated anteriorly and posteriorly. Carapace trapezoidal, widest 

 across the posterior margin, with nearly straight sides. The 

 anterior margin projects slightly between the frontal plates, 

 while the posterior margin has a wide central lobe and narrow 

 and rather pointed lateral lobes. The lateral areas are also 

 narrow and no grooves are anywhere visible on the dorsal 

 surface. 



The dorsal plates of the fused second and third seg- 

 ments have a combined width equal to that of the carapace. 

 Each is elliptical, much longer than wide, and the two are 

 entirely separated along the midline. The plates of the 

 fourth segment are considerably larger; each is orbicular, 

 about as wide as long, and the two are fused at their bases ; 

 they overlap at the center änd have a combined width equal 

 to that of the genital segment. 



