M Y S I D E A. (537 



The third (Sceletinince) , without branchial appendages, and with the 

 inner antennas simple, and the outer two-branched without a proper 

 basal scale. 



The MysiwR have a cavity formed beneath the posterior part of the 

 cephalothorax by plates from the bases of the legs for carrying the 

 eggs before they are fully developed. 



The known genera and subdivisions of the Mysidea, are as fol- 

 lows: 



FAM. I. EUPHAUSnm 



G. 1. NOCTICULA, Thompson* Oculi symmetric!, breves. Pedes thoracis qua- 

 tuordecim, duobus posticis obsoletis branchiis exceptis. Flagella duo antennarum 

 internarum elongata. 



G. 2. EUPHAUSIA, Dana. Oculi symmetric!, breves. Pedes thoracis non ungui- 

 culati, numcro duodecim, quatuor posticis obsoletis branchiis exceptis. Flagella 

 duo antennarum internarum elongata. Segmentum abdominis posticum acumi- 

 natum. 



G. 3. CYKTOPIA, Dana. Oculi paulo oblongi, apice externo oblique gibbosi, 

 lenticulis totis in gibbositatem versis. Articulus antennarum internarum primus 

 apice inferiore productus. Segmentum abdominis posticum obtusum aut trun- 

 catum. 



FAM. II. MYSIDJE. 



SUBFAM. 1. CYNTHIN^E. Pedes abdominis appendicibus branchiali- 

 bus instructi. Antenna) internae biramese, externse squama basali 

 instructge. 



G. CYNTHIA, Thompson.-f Pedes thoracis quatuordecim, biramei; maxillipedes 

 quatuor. Oculi breves symmetrici. 



SUBFAM. 2. MYSIN^E. Pedes abdominis appendicibus branchialibus 

 carentes. Antennae internee birameaa, externae squama basali 

 instructs. 



* Thysanopoda of M. Edwards. The genus Nocticula of Thompson (Zool. Researches, 

 p. 52, pi. 5, f. 1) is identical either with Tliysanopoda or Euphausia, and, as he states 

 the number of pairs of thoracic legs to be eight, it must be identical with the former. 

 The specimens were obtained in the northern Atlantic. 



f Zoological Researches, 55, pi. 6. 



160 



