202 THE VOYAGE OF H.M.S. CHALLENGER. 



pyriform. Autenuular peduncle of usual form ; male appendage rather large. Antennal 

 scale lanceolate, setose on both edges, with a short apical articulation. Mandibles without 

 any distinct molar protuberance. First pair of maxillae with inner lobe very small ; 

 second pair wanting the inner setiferous expansion of the basal part ; terminal joint 

 of palp oblong, not incurved ; exognath very narrow. Maxillipeds and gnathopoda 

 powerfully developed. Legs subequal, comparatively short and stout, with the joints 

 partly appressed, propodal joint subdivided into three articulations, terminal joint 

 having a slender, setiform claw. Marsupial pouch composed of three pairs of incubatory 

 lamellae, anterior pair very small. Male sexual appendages short and thick. Caudal 

 limbs in male all natatory. Telson comparatively short, subtriangular, apex entire, 

 or cleft. Uropoda with inner plate much shorter than outer ; auditory apparatus well 

 developed. 



J^emarls. — This genus, established by the author as early as 1864, is chiefly 

 characterised by the form of the antennal scale, the structure of the mandibles and of 

 the maxilljE, the comparatively robust form of the legs, finally by the form of the telson. 

 From the genus Ili/sis, to which it has some resemblance in its general aspect, it is easily 

 distinguished by the caudal limbs in the male being all natatory. To the genus Promysis 

 of Dana it would seem to be nearly allied, if not actually the same. But, as Dana says 

 that the terminal part (" tarsus ") of the legs in Promysis is not subdivided, whei'eas in 

 all species of the genus Mysido2)sis it is distinctly triarticulate, I have not felt warranted 

 in identifying th(i two genera. Moreover, the species of the genus Prvmysis are pelagic, 

 whereas those of Mysidopsls are true bottom forms. 



Three northern species, viz., Mysidopsis didel'phys, Norman, Mysidopsis gibbosa, G. 0. 

 Sars, and Mysidopsis angusta, G. 0. Sars, have hitherto been recorded, and on the 

 Challenger Expedition a fourth species, ajaparently belonging to the present genus, has 

 been procured and will be described below. 



52. Mysidopds incisa, G. 0. Sars (PI. XXXV. figs. 21-23). 



Mijaidopsis (?) incisa, G. 0. Sars, Preliminary Notices on the Challenger Schizopoila, No. 49. 



Specific Characters. — Form of body rather slender. Carapace small, exposing the 

 .two posterior segments of trunk, frontal margin but slightly projecting in the middle. 

 Last caudal segment longer than preceding. Eyes large, cornea much expanded and 

 deeply emarginate above. Antennal scale narrowly lanceolate. Legs comparatively 

 feeble, with the joints only slightly expanded. Telson shorter than last segment, lateral 

 edges denticulate throughout, apex deeply cleft, incision occupying about one-fourth of 

 the length of the telson and bordered with delicate spinules ; terminal lobes pointed, with 

 apical spines not stronger than lateral denticles. Length, 8 mm. 



RemarJcs. — I have felt warranted in referring this form to the genus Mysidopsis. 



