ZOANTHARIA 



45 



according to the micro-type, and the 12th mesentery from the endocoele of the micro-directive mesenteries 

 was a macro-mesentery instead of a micro-mesentery. 



In the sexual region the macro-mesenteries are short and reach only a little way into the 

 gastrovascular cavity. Their mesoglcea is fairly well-developed. The longitudinal musculature forms 

 few but fairly deep folds. The parieto-basilar muscles are weak and unfolded. The micro-mesenteries 

 are moderately developed with muscles as on the macro-mesenteries. 



The filaments have the typical structure. The glandular tract contains many uniformly broad 

 nematocysts with greatly twisted thread (length 32 — 38//, breadth n — 12 ft). In the type-specimen I 

 found also some very small oval nematocysts (length 17^, breadth 7 p). Further, the glandular tract 

 contains fairly many thick-walled nematocysts with distinct basal part to the spiral thread, which are 

 broader at the one end (length 17—22/*). 



The animals are dioecious. The macro-mesenteries bear as usual the sexual organs. On the 

 1st couple of macro-mesenteries reckoned from the directive micro-mesenteries these are weaker than 

 on the other proto-mesenteries, and the same applies to the youngest meta-macro-mesenteries. 



Isozoanthus davisi n. sp. 



PI. 2, fig. 17. PI, 7, fig. 1. 



Occurrence: Davis Straits 66° 35' N., 56°38 / W. 318 Dan. fins. Bott. temp. 3-9°. Ingolf Expedition 

 St. 32 several specimens (together with /. bulbosus and Epizoaiitiuts lindahli). 



Dimensions: The length of the polyps reached up to 1-40111., largest breadth about 0-4 cm. 

 in the contracted state. 



Colour in alcohol: light or dark sand-coloured. 



External appearance. The majority of the specimens formed small colonies consisting of 

 a few polyps connected with each other by a small, generally thin ccvnenchyme and attached to 

 small yellowish, sometimes branching sand-tubes (of Rhizammina?). All the polyps were probably 

 attached to such objects, though in one case it looks as if the colony was free, probably arising from 

 the fact that a piece of the ccenenchyme is worn off. The polyp is narrowest at the base, from which 

 part it becomes more or less wide upwards, according to the more or less state of contraction. The 

 capitular furrows are very indistinct. The whole body-wall and ccenenchyme of the polyps is richly 

 incrusted with sand-grains, here and there also sponge-needles occur, especially in the uppermost part. 



The tentacles are short. 



The oesophagus is short, the siphonoglyphe distinct with well-marked hyposulcus of almost the 

 same length as the oesophagus. 



Anatomical description. The ectoderm of the body- wall does not seem to be very high 

 except in the capitular region. It is mostly absent and if present filled with detritus and incrusted. 

 Nematocysts with greatly twisted thread 38 — 48^ long and 11 — 12^ broad are fairly common in the 

 proximal part, but very scarce distallv. Further, the ectoderm of the body-wall contains egg- 

 shaped nematocysts resembling those in the filaments (length 22 — 26 p, breadth 5 — 7^). The mesogloea 

 is thick, several times thicker than the ectoderm and contains numerous, scattered large cells, generally 



