3 



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 (Eunicella) 



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 doublé spindles predominating. Euplexaura 



The writer is un.ible to lïnd any character in the definition of the gemis 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, wilh ronnd branches. Axis horn-like. Ccenenchyma moderately 

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

 verrucje. 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 Academy of Science, Vol. I, Part 2, p. 414). 



Synoptic view of the genera and species of the Siboga 



collection of Plexaurid.e. 



*The asterisk (*) denotes a new genus or species. 



Plexaura. 



*P. aggregata, *P. attemeala, *P. recta, *P. 

 p/atystoma, *P. pinnata, 'P. fiava. 



Plexauroides. 

 P. praelouga, P. lenzii. 



Euplexaura. 

 *E. rubra, *E. mollis, *E. reticulata. 



Hicksonella. 

 *H. princeps. 



Psammogorgia. 

 P. arbuscula. 



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

 appear to be new, and nearly half of the total number belong to the type genus, Plexaura. 

 This genus has heretofore been unrepre.sented in the East Indian Region, with the exception 

 of one species which Thomson and Henderson identify as a variety, (flexuosa) of P. antipathes. 

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

 described beyond. 



Systematic discussion of genera and species. 

 Plexaura Lamouroux (emended). 



Plexaura Lamouroux. Histoire des Polypiers coralligènes flexibles, 1 8 1 6, p. 424. 



Plexaura Lamouroux. Exposition Méthodique, 1S21, p. 35. 



Plexaura Milne Edwards et Haime. Histoire Naturelle des Coralliaires, Vol. 1, 1857, p. 152. 



