SYSTEMATIC SURVEY SCYPHOMEDUS^. 173 



and are divided into two groups, Trachomedusae and Narcomedusse, 

 according to the position of the gonads. The fresh-water medusa 

 Limnocodium and Limno- 

 cnida may possibly belong 

 to this group. 



Geryonia,) Carmarina, 

 Cumna, Aeginopsis. 



2. Order Siphonophora. 

 Free-swimming colonies 

 of modified medusoid per- 

 sons (medusomes), with 

 much division of labour. 



Physalia (Portuguese 

 man-of-war), Diphyes, Vel- 

 ella, Porpita. 



Incerta sedis. Grapto- 

 lites. Extinct unattached 

 colonies with a rod -like 

 axis found in Upper 

 Cambrian, Ordovician, and 

 Silurian systems. The 

 colony is usually linear, 

 and consists of cup-shaped 

 hydrothecse borne on one, 

 two, or four sides of the 

 solid axis (virgula). Each 

 opens into a common 

 median canal. At the 

 proximal free end there 

 is a minute triangular 

 or dagger - shaped body 

 the sicula which re- 

 presents the embryonic 

 skeleton. Some repro- 

 ductive bodies or gon- 

 angia have been found. 



The animals were prob- 

 ably free - swimming in 

 muddy seas, and of a 

 Hydromedusan nature. 



FlG. 90. Campanularian Hydroid. 

 After Allman. 



H., Hydrotheca or polyp-cup ; HY., hy- 

 dranth, or polyp-head; G., gonotheca, 

 enclosing a reproductive polyp producing 

 medusoid buds ; Af. t a liberated medu- 

 soid ; ST., basal stolon. 



Class II. SCYPHOMEDUSJE ( = Acraspeda) 



Jelly-fish with gastric filaments, sub-genital pits, and no velum 



(1) Lucernarise. Sedentary forms. Lucernarza, Halzclystus, and 



Depastrum. 



(2) Discomedusse. Active lorms, often with complicated life 



history. Aurelia^ Pelagia, Cyanea, Rhizostoma. 



12 



