292 APPENDIX. No. XL 



probably extensile processes, and separated from its neighbour 

 by a deep notch. The condition of the specimen, whose 

 transparency was lost by its preservation in alcohol, rendered 

 it impossible to determine anything regarding lithocysts, 

 while my unwillingness to destroy a unique specimen has 

 rendered the determination of some other points of structure 

 not so complete as I could have wished. Each tentacle 

 corresponds to one of the notches which separate the marginal 

 lobes. The tentacles are manifestly very extensile, but are 

 easily detached, and had mostly fallen from the specimen. 

 They have the cavity divided into chambers by close septa, 

 and show a very distinct longitudinal fibrillation of thei? 

 walls. The velum is wide and strong. The eight radiating 

 canals with their large oval reproductive sacs are very distinct, 

 but the circular canal, in consequence of the opaque con- 

 dition of the specimen, was but faintly indicated. 



The specimen appears to be a male. 



There can be little doubt that Ptychogastria polaris is 

 the planoblast of some hydroid trophosome as yet unknown. 



Ptychogastria. 



Gen. Char. Umbella hemispherical, with lobed margin 

 and filiform tentacles ; lithocysts ? ; velum broad ; manu- 

 brium short and wide, carrying a wide mouth with quadran- 

 gular lip ; inner walls of manubrium thrown into eight longi- 

 tudinal folds, along whose free edge runs a thick convoluted 

 gland-like chord ; radiating canals, eight ; reproductive sacs 

 oval, large, developed near the middle point of each radiating 

 canal. 



Ptychogastria polaris. 



Umbella about half an inch in diameter ; marginal 

 tentacles numerous (32 ?) 



Captured in Discovery Bay. Captain Feilden. 



