AND RELATED GENERA, SCOTTISH NATIONAL ANTARCTIC EXPEDITION. 261 



thickened on the outer side. On the first 20 mesenteries the pennons of the longi- 

 tudinal muscles well developed. One oesophageal groove. 



H. pilatus M'Murrich. 



H. carlgreni* M'Murrirh (Endoccelactis sp. Carlg.). 



Genus Porponia R. Hertwig. 



Endoctelactidse with (54 ? to) ca. 68 mesenteries, of which 44 perfect. Five cycles 

 of mesenteries. The mesenteries of the fourth and fifth order are regularly arranged, 

 but show unequal development, so that the mesenteries of the fourth order on the one 

 side of the mesenteries of the third order consist of a perfect and an imperfect 

 mesentery, on the other side only of an imperfect mesentery ; but the mesenteries 

 of the fifth order are not paired, and only developed between the mesenteries of the 

 first order and the perfect mesenteries of the fourth order (as in Actinostola). The 

 arrangement of the perfect mesenteries is 20 (6 + 4 pairs) +16 (8 pairs) +8 (these 

 form pairs with imperfect mesenteries). The body goblet-like, sometimes cylindrical. 

 The tentacles on the outer side bridge-like and greatly thickened. The pennons of the 

 longitudinal musculature on the mesenteries hardly indicated. Two oesophageal grooves. 



P. elongata R. Hertwig. 

 P. robusta R. Hertwig. 

 P. antarctica Carlgren. 



Genus Synhalcurias Carlgren. 



Endoccelactidae with considerably more than 68 mesenteries (ca. 100), all of which 

 are perfect, arranged in pairs, and frequently agreeing in the size and distribution of 

 the sexual organs. The irregular arrangement of the mesenteries probably due to the 

 development of the mesenteries of the second and third order in the endocoels. Origin 

 of the mesenteries of the fourth order and the following (?). The body cylindrical. The 

 tentacles are not thickened on the outer side. The longitudinal muscles of the mesen- 



o 



teries weak, not forming pennons, and almost equally developed on all mesenteries. 

 One cesophageal groove (2 ?). 



S. elegans (Wassilieff). 



In a coming work I intend to give a description of the other Actiniaria, ca. 20 in 

 number, which have been collected by the Scotia Expedition. 



* As further characterisation of this species, I may give the following information about the nematocysts : 

 Spirocysts occur in quantities, especially in the tentacles, but are also common in the body-wall, the ectoderm of the 

 oesophagus and in the lil.-iments. They are of greatly varying sizes, generally as large as the corresponding thick- 

 walled nematocyst capsules ; hut smaller as well as still larger ones occur, the latter especially in the tentacles, where 

 they reach a length of up to 43 ^, breadth 7 /*. In the body-wall the thick-walled nematocysts reach a length of 

 22-26 /*, in the tentacles 20-34 ^, and in the filament and oesophagus ca. 26-29 ^. In the latter places are also found 

 nematocysts with distinct basal part to the spiral thread, of almost the same length as the preceding, but broader at 

 the basal end. Tin- thick-walled nematocysts are most numerous in the tentacles. 



(ROY. soc. KUIN. THANS., VOL. L., 69.) 



