iSS The Scottish Naturalist. 



nating abruptly as if broken off (or rudimentary?) External 

 First and second segments short and cylindrical ; third ovate, 

 depressed, and longest ; fourth similar but smaller. The whole 

 furnished with bristles. Feet.— First and fourth pairs robust 

 and much depressed \ the fourth longer than the first ; second, 

 <-hird, and fifth of equal length, and somewhat more than half 

 the length of the fourth ; sixth about one-third the length of 

 the fifth. All are monodactyle, and furnished with bristles on 

 their margii.s. Abdomen. — Cylindrical, excepting the last seg- 

 ment, which is greatly compressed, and longer and deeper 

 than any of the rest. False-feet. — Long, ciliated, decreasing 

 in length backwards, and furnished with filamentous ciliated 

 appendages. Tail. — Telson compressed, grooved above, and 

 rounded at the extremity, which is armed with a sharp spine ; 

 lateral laminae longer than the central-plate, lanceolate, ciliated 

 on their inner margins, the outer ones longest, and rounded at 

 the apex, near to which is a short spine on its lateral margin. 



Only one individual of this species has as yet been found. 

 It was left by the tide at high-water mark, and when found it 

 was of a highly polished opaque white throughout. 



Mysis chameleon J. V. Thompson. — Very common. 



Mysis vulgaris J. V. Thompson. — do. 



Mysis spiritus Norman. — Frequent. 



Mysis sp. 



Thysanopoda couchii Bell. — Common, cast on beach. 



Thysanoessa borealis Norman. — Frequent on sands. 



Thysanoessa aberdonensis, n. sp. 



(Plate V., Fig. i.J 



Carapace. — Smooth, lateral margins terminating in a spine 

 anteriorly, posterior margin roundly indented. Rostrum. — 

 Straight, with a ridge along the median line, which forms the 

 point of the rostrum. Orbits. — Open above. Eyes. — Large, 

 set on short and very slender peduncles, which do not extend 

 beyond the orbits. External antenna. — First segment nearly 

 one-fourth the length of the antennal scale \ second and third, 

 somewhat over three-fourths the length of the scale ; movable 

 portion, including the three segments, twice the length c/. the 



