Spicules. The spicules are mainly spindles, straight and curved, relatively large as 

 compared with most of the others in the Siboga collection of this genus, but not so as compared 

 with some other Plexauridae. A few club-shaped forms are present. 



Color. The colony is a light naples yellow, probably brighter when fresh. The axis is 

 brown and the spicules colorless. 



This species differs in general appearance from the other species of Plexaura in the 

 collection, but the writer is unable to find any structural difference, unless it be in the spicules, 

 which do not seem of a sufficiently different type to warrant its exclusion from the genus. 



Plexauroides Wright and Studer (emended). 



Plexauroides Wright and Studer. Challenger Reports, the Alcyonaria, 1889, p. 138. 

 Plexauroides Studer. Alcyonarien aus der Sammlung des Naturhistorischen Museums in Liibeck, 



1894, p. in. 



Plexauroides Brundin. Alcyonarien des zool. Museums in Upsala, 1896, p. 19. 

 Plexauroides Kiikenthal. Japanische Gorgoniden, II. Teil, 1909, p. 27. 



The original definition of this genus is as follows : 



"Colony branching, mostly in the one plane. Stem and branches cylindrical. Axis horny 

 dense, with the central portion calcareous. Nutrient canals symmetrically arranged. Coenenchyma 

 thin, consisting of two very distinct layers of spicules, the one nearest the axis is composed of 

 irregular stellate forms, the outer layer of large Blattkeule, the broad foliar expansions of which 

 project beyond the surface of the coenenchyma forming a rough imbricated surface". 



The polyps are numerous, fully retractile, with scarcely visible verrucse, the edges of 

 these latter being fringed with rows of the broad projecting folia of the Blattkeule. 



KUKENTHAL re-defines the genus so as to exclude Plexauroides verrucosa Brundin, and 

 P . asper Moroff, which he places in a new genus Paraplexaura, which he differentiates from 

 Plexauroides mainly on account of short terminal branches and true calyces. 



Aside from the original definition, there is no reference to the calcareous core to the 

 axis, and it is not referred to by BRUNDIN in his discussion of the genus. The specimens in the 

 Siboga collection do not show this character, but there is a white core to the axis which is 

 not calcareous. It may possible have deceived the describer of the genus, as it looks very 

 much like a calcareous core. 



The spicules are the characteristic feature of the genus, which may be described as follows : 



Plexauridae with a horny axis, long terminal branchlets inserted calyces, ccenenchyma 

 rather thin, but composed of two very distinct layers of spicules. The outer layer is formed of 

 spicules whose proximal part bears branched, warty radiating processes projecting downward 

 and outward ; and whose distal portions are composed of broad, leaf-like expansions standing at 

 right angles to the surface of the branch when in situ. The inner layer of spicules is composed 

 of smaller cruciform or stellate forms. 



The type of this genus is Plexauroides pr&longa (Ridley). The other known species are 

 Plexauroides indica Ridley, P. unilateralis Studer, P. lenzii Studer, P. michelsoni Kiikth., 

 P. rigida Kiikth., P. simplex Kiikth. and P. filiformis Kiikth. 



SIBOGA-EXPEDITIE XIII *'. 2 



