28 



Eyes large : eyestalks with a small tubercle on their inner face. The basal 

 joint of the antennular peduncle is broad and triangular, and is hollowed for the 

 reception of the eye : its outer edge is produced anteriorly into a spine, but there 

 is no scale on its inner border. 



Of the two antennular flagella the outer (upper) one is compressed sub- 

 foliaceous and extremely short and arises near the base of the terminal joint of 

 the peduncle, while the inner (lower) one is cylindrical and extremely long and 

 springs from the apex of the terminal joint of the peduncle. 



Antennal scale large, its outer edge strong and anteriorly acute : antenna! 

 flagellum very long. 



The mandibular palp is foliaceous, but not broadly so, and of moderate 

 length, barely reaching the antennular sternum : its terminal joint, which is more 

 or less triangular, is much shorter than its basal joint. Palp of the first maxilla? 

 single jointed. 



The exopodite of the 2nd maxillipeds is much longer and stouter than that 

 of the external maxdlipecls the exopodite of the latter being lax and slender. 



The external maxillipeds are long and pediform. The first 3 pairs of 

 thoracic legs are chelate with the fingers long and slender, usually much longer 

 than the palm : the last 2 pairs are slender and monodactylous. 



There are usually no exopodites to the thoracic legs, but minute ones are 

 sometimes present. 



The abdominal appendages are slender, the exopodites being vastly longer 

 than the endopodites. In the first pair no endopodite is present, but in the ■ 

 male there is a triangular or subtriangular " petasma " or " andricum." In the 

 second pair the endopodite carries at its base, in the male, a pair of little scales, 

 one behind the other. The first 3 abdominal sterna are prominent and more or 

 less acute in the middle line. 



Epipodites are present on the first 3 or 4 and podobranchire on the first 2 

 or 3 thoracic legs, and small or quite rudimentary pleurobranchiae on most of 

 the thoracic somites, the last pleurobranchia however (on somite XIV) being of 

 normal size. In the subgenus Arisiaeopsis alone do the other pleurobranchia? 

 approximate to normal size. 



The species of Aristaens may be grouped into five subgenera as follows: — 



Synopsis of the subgenera of Aristreus. 



I. No hepatic spine. Rostrum 3-toothed (occasionally 2-4-toothed) :— 

 1. The third pair of thoracic legs have an epipodite but no podo- 

 branch, the 4th pair have no epipodite : — 



i. Cervical groove indistinct; the pleurobranchise in 

 advance of the functional one on somite xiv are 

 mere filaments or papilla? ... ••• Akist>eus. 



