JtEha. 315 



mandibles are strong, horny, curved inwards at the tip, 

 and armed with several teeth, the lowest of which is 

 truncate. They are provided with a three-jointed palpi- 

 form appendage. The basal joint of the foot-jaws is 

 large and triangular, with the tip ciliated, followed by 

 five joints, of which the distal ones are the most slender. 

 The first pair of maxillas are furnished at the extremity 

 with three oval membranous plates, ciliated at their 

 extremities, the anterior one being the largest. The 

 second maxillae are composed of two branches, of which 

 the outer one is the larger, and armed at the tip with 

 strong bearded bristles. 



The segments of the body are strongly marked by 

 lateral incisions, the sides being rounded, and the pos- 

 terior-lateral margins not produced into a point. The legs 

 are of moderate size, being nearly uniform both in length 

 and thickness, and terminated by two small hooks of 

 nearly equal size. The female carries between the base 

 of the legs an ovigerous pouch, composed of delicate 

 membranous plates, within which the young are deve- 

 loped. The tail consists of only a single plate, formed by 

 the coalescence of all the segments of the pleon, which is 

 semicircular (or semi-ovate) in form, and, in our British 

 species, with a small semicircular incision in the middle 

 of the posterior margin, within which are attached the 

 two very minute terminal appendages, each of which 

 consists of a square flat joint, supporting two extremely 

 minute conical plates, of which the outer one is almost 

 obsolete ; the tips of these plates are furnished with 

 hairs. In /. Kroyerii the tail has two small semicircular 

 incisions, between which the centre is produced into a 

 small point, and the appendage on each side consists of a 

 small square basal joint, supporting two minute oval 

 plates. 



