iSi 



somites were distinct beneath the carapace in Pygocephalus, but in 

 the genus Crangopsis of Salter, from the Lower Carboniferous, 

 Ortmann has shown that at least four somites are distinct. It 

 is probable that other fossil genera, such as the Carboniferous 

 Anthrapalaemon, may be found to possess Mysidacean characters. 



AFFINITIES AND CLASSIFICATION. 



The removal of the Mysidacea from their old association with 

 the Euphausiidae in the group " Schizopoda " is 

 justified by the fact that the two groups do not 

 have in common any characters except those of 

 the primitive caridoid facies which they share 

 with the lower Decapoda and, in part, with the 

 Stomatopoda. On the other hand, the con- 

 nection of the Mysidacea, through the Cumacea 

 and Tanaidacea, with the Isopoda and Amphi- 

 poda is shown not only by the characters given 

 in the definition of the division Peracarida, but 

 also by many connecting characters which link 

 together the individual orders. For example, 

 the retroverted palp of the maxillula in Gnatho- 

 phausia is repeated in the Cumacea and Tanaidacea, 

 and th& branchial epipodite of the first thoracic 

 limb in these two orders may be derived from 

 the simpler appendage found in the Mysidacea. 



The families mentioned below are those 

 accepted by G. 0. Sars, with the addition of 

 the Petalophthalmidae, established by Holt and Tattersall (following 

 Czerniavsky). The sub-families of the Mysidae as adopted here 

 have been regarded by Norman as distinct families. 



Fio. 110. 



Pygocephalus Cooperi, 

 from the Coal-measures. 

 Female specimen, from 

 below, showing the imbri- 

 cated oostegites. (After 

 Woodward.) 



ORDER Mysidacea, Boas (1883). 



Family LOPHOGASTRIDAE. Lophogaster, M. Sars ; Gnathophausia, 

 Willemoes - Suhm (Fig. 100). Family EUCOPIIDAE. Eucopia, Dana. 

 Family PETALOPHTHALMIDAE. Petalophthalmus, Willemoes-Suhm ; Han- 

 senomijsis, Stebbing. Family MYSIDAE. Sub-Family ARCHAEOMYSINAE. 

 Archaeomysis, Czerniavsky. Sub-Family LEPTOMYSINAE. Leptomysis, 

 G. 0. Sars ; Erythrops, G. 0. Sars ; Dactylerythrops, Holt and Tattersall ; 

 Euchaetomera, G. 0. Sars ; Amblyops, G. O. Sars ; Pseudomma, G. 0. Sars. 

 Sub-Family ARACHXOMYSINAE. Arachnomysis, Chun. Sub-Family 

 MYSIDETINAE. Mysidetes, Holt and Tattersall. Sub-Family MYSINAE. 

 Mysis, Latreille (Fig. 99) ; Macromysis, White ( = Praunus, Leach). Sub- 

 Family STILOMYSINAE. Stilomysis, Norman. Sub-Family HETEROMYSINAE. 

 Heteromysis, S. I. Smith. Sub-Family MYSIDELLINAE. Mysidella, G. O. 



