X.OANTHARIA 



39 



The filaments have the usual structure. The glandular tract contains numerous nematocysts 

 with much coiled thread 26 36^ long and 10 i2// broad, sometimes even narrower. Further, some 

 thick-walled capsules are found (length 19 22//). 



The colony was not sexually ripe. 



Genus Isozoanthus Carlgren. 



Isozoanthus n. gen. Carlgren in Nordgaard Hydrogr. and Biol. Investig. 1905 p. 159. 

 Macrocnemic Zoantheae with a diffuse entodermal sphincter muscle. The body-wall incrusted. 



The ectoderm is always continuous. Cell-islets and lacunae in the mesogloca but no encircling sinus. 



Dioecious polyps. Polyps solitary or in small clusters, as a rule connected with a comparatively thin 



cojiienchyme. 



The genus, which has been briefly characterised by me on an earlier occasion (1905 p. 159), 

 forms a link between the genera Epizoanthus and Parazoanthus. With regard to the appearance of 

 the sphincter, Isozoanthus agrees with the latter, but in the structure of the body-wall it agrees with 

 the former. In the genus Isozoanthus the encircling sinus so characteristic of Parazoanthus is wanting. 

 If attention is only paid to the appearance of the sphincter in arranging the genera within the 

 macrocnemic Zoanthidae, the Isozoanthus-species would have to be referred to the older genus Para- 

 zoanthus, but if the structure of the mesoglox-a of the body-wall is considered to be of some importance 

 in the characterisation of the genera, it is most reasonable to let the species, which have no incircling 

 sinus but are otherwise in the main in agreement with Parazoanthus, form a separate genus, i. e. 

 Isozoanthus. In the latter case the diagnosis given by Had don and Shackleton for the genus 

 Parazoanthus would need no revision, in the first case on the other hand their diagnosis would have 

 to be altered with regard to the encircling sinus, as for example "encircling sinus absent or present" 

 If the species comprised by me under the genus Isozoanthus are referred to the genus Parazoanthus. 

 it would at any rate be advisable to let them form a separate sub-genus named Isozoauthus. Future 

 investigations must decide, whether Isozoanthus should be considered a separate genus or a sub-genus. 

 The type for the genus Isozoanthus is Isozoanthus (Epizoanthus) arborescens (Dan.). Another 

 species, by the way the longest Zoantharia known, has been figure by me in Chun's work: "Aus 

 den Tiefen des Weltmeeres" 2 Aufl. 1905 p. 520. It has been dredged on the Agulhas Bank during 

 the German deep-sea expedition and provisionally named by me /. giganteus. The genus thus occurs 

 in northern as well as in southern seas. A revision of the Zoanthidae already described would pos- 

 sibly show, that certain forms described as Parazoanthus should in reality be referred to Isozoanthus. 

 Of the 9 Isozoanthus-species mentioned here only one, namely the type of the genus, /. arbo- 

 resccnj, has been described before by Danielssen, who referred it to the genus Epizoanthus. Da- 

 niel ss en's anatomical description leaves much to be desired in many respects. All the species with 

 exception of /. danicus have been dredged during the Ingolf Expedition. /. danicus has been taken 

 in the Limfjord and determined by Morten sen (1897) as Z. couchii (Johnst). 



