MYSIDEA. 643 



Carapax very short rostrate. First joint of inner antennae oblong and 

 produced at apex. Basal scale of outer antennae shorter than base. 

 Feet very slender, last three joints subequal, and together but little 

 shorter than preceding joint, setae long, short plumose, palpus not 

 half as long as leg. Last segment of abdomen longer than caudal 

 lamellae, the two subapical barbs salient, sixth segment about twice 

 as long as fifth. Posterior branchiae ramose. 



Plate 42, fig. 5 a, animal, enlarged ; 7), extremity of abdomen ; c, 

 fourth pair of legs ; d, sixth pair ; e, posterior pair of branchiae ; /, 

 first pair of abdominal legs ; g, second pair, ditto ; /*, third pair, ditto. 



Abundant in the Atlantic in latitude 2 north, longitude 17 west. 

 October 29, 1838, at 4 A. M. There were many Pyrosomas floating 

 by at the time, and few Cyclopidoe. Found none on the afternoon of 

 the same day, and the morning of the day following. 



Length, about half an inch. Colour, reddish about ventral parts. 

 Carapax a little compressed, not toothed, and vertical height not 

 much less anteriorly than posteriorly. Sixth joint of abdomen about 

 as long as two preceding. The inner antennae have a three-jointed 

 base about three times as long as the eye. The flagella of both pairs 

 of antennae were broken in all the specimens (some fifteen or twenty) 

 collected, so that the full length was not ascertained they are probably 

 not very much longer than the carapax. The ciliae of the oblong scale 

 of the outer antennae are curled at apex. The branchiae of the anterior 

 legs consist of a cluster of small vessels, while the posterior are larger 

 and branched, main branches three or four in number; none were 

 observed on the first pair. The palpus or natatory branch of the 

 legs is longest upon the anterior pairs. The main stem of these legvs 

 appears to have little lateral motion. The last three joints have u 

 row of long plumose cilioe on the inner side, while the preceding have 

 two or three rows of similar ciliae or hairs. 



The two anterior pairs of abdominal legs are peculiar in form. The 

 outer branch of the first pair is large, and has a gibbosity on the inner 

 side, and is consequently obliquely excavate under the acute apex; the 

 other branch is lanceolate and ciliated. The second pair somewhat 

 resembles the first, but is more slender; there appeared to be a scale 



