27 



the spinules, the first, which is still preserved, being the shortest and situated somewhat before 

 the middle, while the last, which probably was very long, has been inserted opposite the bottom 

 of the cleft ; each interval between two of these spines is occupied by several small spinules. 



Length of the specimen, an adult male, i6 mm. 



Remarks. — B. inerinis is easily distinguished from all other species of Boreomysis 

 by having the naked part of the outer margin of the e.xopod of the uropods so unusually short 

 as described above. The shape and armature of the telson show other valuable characters. 



Subfamily II. Siriellinae Norm. 



The essential characters are given in the synopsis on p. 1 1 . But some other features 

 may be mentioned. Body slender. Carapace short or very short. Eyes well developed. Antenna! 

 squama with the outer margin naked and terminating in an acute' tooth. Mandibles with the 

 molar tubercle feebly developed, sometimes shaped as a distally blunt process; the development 

 of the cutting edge, the lacinia mobilis and the setae exceedingly varying. Maxillae narrow; lobe 

 from third joint feebly cleft; exopod rather small; distal joint of the palp very oblong, longer 

 than the proximal joint. Maxillipeds somewhat slender; the lobe from second joint rudimentary 

 or wanting. Gnathopods simple; sixth joint very oblong. 



Fig. I h on pi. VI shows the arrangement of the setae constituting the terminal brush 

 on sixth joint of the thoracic legs; each seta consists of a basal glabrous part and a distal 

 much longer portion built in the most peculiar way. On fig. i i a. shows the terminal part of 

 a seta seen from above, and b. the same seta from the side, and it is easily seen that the 

 seta itself seems to be furnished with a not quite close row of plates which seen from the side 

 are similar to very flat cups. 



Only a single genus, Siriclla Dana, was hitherto known. The "Siboga" captured an 

 enormous material of the subfamily; the major part belongs to Siriclla, but a couple of species 

 are so aberrant, that a new genus, Hemisiriella, is to be established for their reception. 



Key to the Genera. 



First pair of thoracic legs at least slightly shorter than second pair, with the 

 "claw" (seventh joint + the real claw) very well developed. The carapace 

 covers at least a part of the sides of the penultimate thoracic segment. Siriella Dana. 



First pair of thoracic legs extremely elongated, almost twice as long as the 

 second pair, with the "claw" rudimentary. The carapace unusually short, 

 not covering any part of the penultimate thoracic segment Hemisiriella n. gen. 



Siriella Dana. 



In his work on the Mediterranean Mysidae G. O. Sars gave a very elaborate description 

 of this genus. In the key the main characters distinguishing this genus from Hemisiriella n. gen. 



