682 Reports on the Zoological Collections made in Torres Straits, 1888-1889. 



Canals are present from the oesophageal region downwards, frequently two or 

 three in the perfect mesenteries. These canals are connected with the canals of 

 the body-wall at the base of the column. Nematocysts are numerous in the 

 endoderm of the mesenteries. The longitudinal muscle fibres form a simple 

 layer, the parieto-basal muscles are better developed and supported upon slightly 

 branched plaits of mesogloea. 



Gonads. — No gonads were present in the specimens we examined. 



This species cannot be mistaken for either of the two previously described. 



ISAXJRUS, Gray, 1828. 



Antinedia, Duch. & Mich., 1866. 

 PoLYTHOA (Monothoa) (pars), Andres, 1884. 

 ZoANTHUS (MoNANTHUs) (pars), Andres, 1884. 



Large brachycnemic Zoanthese with a single mesogloeal sphincter muscle. 

 The body- wall is unincrusted; the ectoderm discontinuous; ectodermal and 

 endodermal bays and small canals in the mesogloea. Monoecious or dioecious. 

 Polyps in small clusters or solitary. 



The genus Isaurus was established by J. E. Gray in 1828 (Spic. Zool., 1828, 

 p. 8) to include a species not before described, specimens of which from an 

 unknown locality were in the British Museum. He named this species Isaurus 

 tuherculatus on account of the tubercles on its surface. The name Isaurus is a 

 Latinized version of Isaure, a name applied by Savigny (Description de I'Egypte, 

 Polypes, pi. 2, figs. 1—4, 1811, ined.) to four species figured by him in 1811, and 

 supposed by Gray to be of the same genus as his /. tuhercidatus. Savigny published, 

 however, neither tlie characters of the genus nor descriptions of the species. 

 Lamouroux mentions the genus as Isaura, but neither does he define it in any 



way. 



The genus Isaurus must therefore be regarded as Gray's, and Isaurus tuhercu- 

 latus as the type species. 



In 1860 Duchassaing and Michelotti found specimens at St. Thomas and 

 Guadaloupe, which closely agreed with Gi-ay's account of Isaurus tuhercidatus. 

 Although unaware of the existence of Graj^'s species, they gave to their specimens 

 the same specific name, calling them Zoanthus tuherculatus, and subsequently in 1864 

 (forming for the species a new genus), Antinedia tuherculata. Andres considered 

 that Gray's /. tuherculatus, and Duchassaing and Michelotti's A. tuherculata, were 

 distinct species, and consequently renamed the latter A. duchassaitigi. 



