distal branches are much longer and more slender than in Isis hippuris, sometimes attaining 

 a length of as much as 17 cm., while their diameter is only 2 mm. The terminal twigs are 

 not swollen at the ends, in marked contrast to /. hippuris. 



The calyces are entirely included, very small, and sparsely and irregularly distributed on 

 all sides of the branches. The polyps are partially expanded in the specimen described, making 

 it difficult to ascertain the form and size of the apertures. Where the polyps are fully retracted 

 the surface of the branch is perfectly smooth, with little or no indication of the calyx openings. 

 The polyps themselves are small and appear to be devoid of spicules, both in body walls 

 and tentacles. Consequently they are very soft and flabby, and are usually prone against the 

 ccenenchyma of the branches when expanded in alcoholic specimens. 



Spicules. The spicules are minute, smaller than in Isis hippuris, and distinctly different 

 in shape, being much more delicate spindles with tubercles often symmetrically disposed around 

 the main axis. Irregular branched forms are common. Crosses are more rarely seen, and also 

 a few curved spindles with large tubercles. A comparison of a slide of spindles from I. reticulata 

 with one from I. hippuris shows a very distinct difference in the assemblage of forms of the 

 two species. 



Color. The entire colony, in alcohol, is reddish brown. The polyps are more distinctly 

 reddish than the ccenenchyma, sometimes approaching a maroon. 



The species seems quite distinct from Isis hippuris, from which it differs in manner of 

 branching, reticulation, slenderness of twigs, color, and most of all in the character of the spicules. 



Ceratoisidinae. (For definition of subfamily see p. 4). 

 Ceratoisis Wright. 



Keratoisis E. Percival Wright. Annals and Magazine of Natural History, 4'h Series, Vol. II, 



1868, p. 427. (Name only). 



Keratoisis E. Percival Wright. Annals and Magazine of Natural History, 4^ Series, Vol. III, 



1869, p. 23. 



Keratoisis Gray. Catalogue of Lithophytes in the British Museum, 1870, p. 18. 



Keratoisis Studer. Monatsbericht der Königl. Akademie der Wissenschaften zu Berlin, 1878^.662. 



Ceratoisis Verrill. Bulletin Museum of Comparative Zoology, Vol. XI, 1883, p. 10. 



Ceratoists Wright and Studer. Challenger Reports, the Alcyonaria, 1889, p. 26. 



Ceratoisis (in part) Hickson. National Antarctic Expedition. Natural History, Vol. III, Ccelentera 



Alcyonaria, 1907, p. 5. 

 Ceratoisis Nutting. Hawaiian Alcyonaria, 190S, p. 570. 



The original description of this genus is as follows : 



"Coral branched, irregularly furcate; axis jointed, composed of horny and calcareous 

 portions; the latter are hollow, smooth, varying considerably in length, and maintaining their 

 form after maceration in caustic alkalies; the branches are given off from the calcareous portions. 

 The so-called "barky layer" (coenenchyma) is well developed, and contains a large number of 

 calcareous spicules. The polyps are irregularly and somewhat densely grouped all around the 



SIBOGA-EXPEP1TIE XIII b*. 2 



