658 Haddon and Shackleton — A .Revision of the British Actinice. 



Cell-islets and lucunse are also often enclosed in the mesogloea. The endoderm 

 forms a thin layer of almost uniform thickness. The diffuse endodermal muscular 

 layer is well developed. 



Sphincter muscle. — The sphincter muscle is diffuse and endodermal, as in other 

 species belonging to this genus. The mesogloeal plaitings are deep and well 

 developed, but they branch very slightly. 



Disc and Tentacles. — There is little worthy of special note in the structure 

 of the disc and tentacles. The ectodermal muscles are exceedingly well 

 developed. 



(Esophagus. — The ectoderm of the oesophagus is generally thrown into folds, 

 but these are in some cases very slight. There is generally a well-marked 

 groove, the mesogloea being here somewhat thickened. Occasionally cell-islets 

 are to be found in this region. 



Mesenteries. — The arrangement of the muscle is macrocnemic. The imperfect 

 mesenteries generally extend well into the coelenteron. The longitudinal muscles 

 vary considerably in the degree to which they are developed, not only in 

 individuals, but in different parts of the same individual. In some cases they 

 form an almost simple layer, whilst in others they are supported on well- 

 developed plaitings of the mesogloea. The filaments are formed by the con- 

 tinuation of the ectodei'm in the usual manner. Immediately below the oesophagus, 

 the perfect mesenteries, bearing the filaments, extend but a short distance into the 

 coelenteron, leaving considerable empty space in the centre. Lower down they 

 again increase in size, and near the base of the polyp they contain sinuses which 

 appear to be of the same origin as the ectodermal enclosures of the body-wall. 



Gonads. — There were no gonads in the specimens of this species which were 

 examined by us. 



Parazoanthus* dixoni, n. sp. 



(PI. Lviii., figs. 37, 38; PI. lix., figs. 9, 10 ; PI. lx., figs, 8, 9.) 



Form. — Body long, cylindrical, or quite short, smooth, or slightly roughened, 

 very few incrustations. Polyps crowded, springing irregularly in all directions 

 from an expanded, soft, thick coenenchyme. Buds often arise from close to the 

 bases of the older polyps. Scarcely any diminution in the length of the 

 contracted polyps is noticeable as compared with the expanded specimens. The 

 upper end of the contracted specimens is swollen, and has about 21 inconspicuous 



* We name this species in honour of our friends the brothers Gr. T. and A. F. Dixon, who have done 

 much valuable work in connexion with the Irish ActiniDS. 



