Coenenchyma thin. Large, bar-like spicules very prominent. . . . Hicksonella 

 Spicules of outer layer clubs or "Blattkeulen"' vertically placed. 



Clubs large. Terminal branches long and .slender Plexauroides 



Clubs small. Terminal branches short (Paraplexaura) 



Clubs minute, their club-ends inflated and free (Eunicellaj 



Axis with a central horny core, around which is a tubular casing containing 

 more or less calcareous matter. 



Spicules large, clubs, crosses and triradiate forms predominating. . . (Plexaurella) 



Spicules small, short oval spindles and double spindles predominating. Euplexaura 



The writer is unable to find any character in the definition of the genus Psammogorgia Verrill by which it can be differentiated 

 from others of the family. He therefore gives the definition proposed by the original describer, which is as follows : 



"■Psammogorgia Verrill. Corallum dichotomous or subpinnate, with ronnd branches. Axis horn-like. Coenenchyma moderately 

 thick, the surface finely granulated with small rough spicula. Cells scattered, sometimes flat, more frequently raised in the form of rounded 

 verruca:. Polyps with rather large, elongated, slender warty spindles at the bases of the tentacles. Spicula of the ccenenchyma mostly short, 

 thick, and very rough, warty spindles and rough, warty clubs of moderate size". 



(Verrill, Transactions Connecticut .\cademy of Science, Vol. i. Part 2, p. 414). 



Synoptic view of the genera and species of the Siboga 

 collection of PLEXAURiD.i;. 



•■'The asterisk (•■■) denotes a new genus or species. 



Plexaura, 



'P. recta, ^P. 

 platystouia, '^P . pinnaia, "P. flava. 



Plexauroides. 



P. praclonga, P. leiizii. 



Euplexaura. 



''E. riibra, *E. mollis, *E. reticulata. 



"Hicksonella. 

 *//. princcps. 



Psammogorgia. 

 P. arbiiseitla. 



The above table indicates that of the thirteen species of the Plexaurida' collected, ten 

 appear to be new, and nearly half of the total number belong to the type genus, P/e.vaiira. 

 This genus has heretofore been unrepresented in the East Indian Region, with the exception 

 of one species which Thomson and Henderson identify as a variety, {ßex7io.<:a) of P. antipat/ies. 

 The present writer is of the opinion that this form is identical with the new species /'. aggregata, 

 described beyond. 



Systematic discussion of genera and species. 



Plexaura Lamourou.x (emended). 



Plexaura Lamouroux. Histoire des Polypiers coralligenes flexibles, 18 16, p. 424. 



Plexaura Lamouroux. Exposition Methodique, 1 821, p. 35. 



Plexaura Milne Edwards et Haime. Histoire Naturelle des Coralliaires, Vol. i, 1857, p. 152. 



