4 Mr. P. W. Bassett- Smith on some 



Bomolochus tetradonis, sp. n. (PI. I. fig. 2.) 



These specimens were found abundantly in the gill-cavities 

 of Tetrodon ohlongus at Bombay ; both sexes were generally 

 present together in the same fish. They resemble somewhat 

 B. gracilis of Heller, which he found on the hammer-headed 

 shark at Java, but differ in detail. By obtaining a large 

 number of specimens it was found to vary very much in 

 form, proportionally of length to breadth, even in mature 

 females, as shown in PI. I. fig. 2 ; so that the mere external 

 conformation is of comparatively little assistance in differen- 

 tiation of the species (in mounted specimens the frontal 

 border always folds backwards and renders examination 

 difficult). 



Female. — Cephalothorax pyriform or elongated, divided 

 into five distinct segments, arched dorsally. First segment 

 shorter than long, second to fifth becoming progressively more 

 so. Anterior antennce arcuate, elongate, bearing on the front 

 edge about sixteen short seta3 with rounded bases ; three free 

 club-shaped joints, the last being provided with many short 

 bristles. Posterior antennce two-jointed, terminating in five (?) 

 short seta\ Hamulus placed far forwards and to the side, in 

 the shape of a very strong, short, thick, slightly curved spur. 

 Mouth-organs are placed between a well-marked upper and 

 lower lip, there being no sharp-pointed rostrum as in the 

 last species ; into this space project three pair of appendages, 

 the most anterior, the mandible, having three joints, the last 

 consisting of a long curved pointed joint, with its convex 

 border finely crenulate and an accessory palp ; the second 

 'h&\i\gih& first ma xilliped^tA^o three-jointed, the first joint being 

 long and cylindrical, the second short, and the third in the 

 form of a strong slightly curved claw ; the third being the 

 second maxillipedj larger, with a thicker basal joint, terminal 

 joints simple, with finely dentate concave margin. 



First four 'perceo'pods two-branched, second to fourth each 

 with three joints, provided with plumose hairs on the 

 inner border and with more or less elongated simple bristles 

 on the outer, that of the second joint of the inner branch of 

 the second pair being very long and strong. 



Fifth perasopod three-jointed, the last joint being provided 

 with three short bristles only. 



Genital segment short and broad. Abdomen couBx^img oi 

 four joints progressively decreasing in size, the last terminating 

 in two caudal plates nearly three times as long as broad, 

 carrying two long terminal bristles and two short lateral ones. 



