TRACHYMEDUS.K. 13 



OLINDIOIDES, Goto, 1903. 



Similar to OlinJias, but with six radial-canals (two bifurcated and two simple). Six 

 gonads. Four lips. The exumbrella tentacles project at various levels from the 

 sides of the bell. 



Family No. 2, PETASIDjE Haeckel, 1879. 



Trachymedusae with tour radial-canals upon which the linear or sac-like gonads are 

 developed. Tentacles without adhesive disks. Four lips. 



PET ASUS = Pftasus + Dif>etasus + Petas(ita + Pftacli>: uni, Haeckel, 1879. 



Tentacles arise at equal intervals, not grouped into clusters. No centripetal canals. 

 Free marginal hthocyst-clubs. 



AGLAUROPSIS, F. Miiller, 1865. 



Similar to Petasus, but the lithocysts are vesicular, and project from the bell-margin 

 between the tentacles. 



CRASPEDACUSTA, Lankester, i$%o=LimnocoJium, Allman, 1880. 



Tentacles arise singly as in Pi-tnsus and Aglauropsis, but the lithocyst concretions are 

 each inclosed in a cavity within the gelatinous substance of the velum on the inner 

 (centripetal) side of the ring-canal. (The medusa lives in fresh water among water- 

 lilies.) The hydroid is devoid of tentacles. 



MlCROHYDRA, PottS, 1885. 



Is possibly identical with Limnocodiutn, but the mature medusa is unknown. The 

 young medusa has no lithocysts, and it arises by budding from a minute hydroid 

 which has no tentacles. 



MJ^OTIAS, OstroumofF, 1896. 



Tentacles arise at equal intervals, not in clusters. Numerous centripetal, blindly-ending 

 canals arise from the ring-canal. 



GOSSEA, L. Agassiz, 1862. 



Tentacles grouped into clusters. No centripetal canals. Lithocyst concretions free or 

 inclosed. 



Family No. 3, LIMNOCNIDIDjE. 



Numerous hollow tentacles which project singly, not in clusters, from the sides of the 

 bell in a zone slightly above the margin. Tentacles without adhesive disks. Numerous 

 inclosed lithocysts on the exumbrella side of the velum. Mouth a round opening. Gonads 

 developed diffusely in the ectoderm of the stomach-wall. Four (occasionally five or six) radial- 

 canals. Medusa-buds arise from the sides of the stomach, and are set free. 



LIMNOCNIDA, Giinther, 1893. 



Generic characters are those of the family. The only known species is /,. tanganjicd 

 from the fresh-water lakes of Central Africa, and the Niger river. 



Family No. 4, PTYCHOGASTRIDJE. 



Numerous more or less isolated clusters of tentacles, some of which bear adhesive disks. 

 Numerous free lithocyst-clubs. Eight radial-canals. Four lips. Stomach eight-lobed. These 

 stomach-lobes are in the radii of the radial-canals, and are bound to the subumbrella by 

 means of eight mesenterial partitions. The gonads are upon the eight stomach-lobes, and 

 each is more or less divided by the mesentery so there may be eight double (sixteen) gonads. 



PTYCHOGASTRIA, Allman, iSfi^Pcctyllis + Pectis + Pectanthis, Haeckel, 1879. 

 The generic characters are those of the family. 



Family No. 5, TRACHYNEMID^E. 



Trachymeduss with eight simple radial-canals upon which the gonads are developed. 

 No mesenterial partitions in the subumbrella. Tentacles without adhesive disks. Ring- 

 canal simple without centripetal branches. 



