SILICIOUS AND HORNY SPONGES WILSON. 277 



SYSTEMATIC DESCRIPTION. 



Order TETRAXONIDA. 



Demospongiae Sollas, 188S, minus Ceratosa. 

 Tetraxonida Dendy, 1905. 

 The characteristic form of spicule is a silicious four-rayed sclerite, 

 each ray representing a particular axis (tetraxonid or tetractinellid 

 spicule). But in some groups these spicules have been lost. 



Suborder Astrophora. 



Astrophora Sollas, 1S88. 

 "With tetraxonid megascleres and astrose microscleres ; without 

 (lesmas. 



The families are : Theneidae, Stellettidae, and Geodiidae. 



Family THENEIDAE. 



Theneidae Sollas plus Paehastrellidae (Carter), Sollas, 1888. 

 Asterostreptidae Topsent, 1902&. 



Stcllcttidae part plus Pachastrellidac Lendenfeld, 1903. 

 Theneidae plus Paehastrellidae Lendenfeld, 1906. 

 Pachastrellidac Hernandez, 1914. 



The characteristic astrose microscleres are streptasters ; oxyasters 

 occur also in some species. The ectosome does not form a cortex. 



I follow Topsent in combining the Theneidae and Paehastrellidae, 

 but it does not appear that the new name Asterostreptidae is neces- 

 sary, unless the old groups are retained as subfamilies. But it seems 

 clear that the genera can not at present be successfully thrown into 

 groups. The family is therefore to be directly divided into genera. 

 As to the choice of name for the combined group, Thenea Gray 

 (1867) antedates Paehastrella Schmidt (1868). 



In addition to the component genera recognized by Topsent, 19025 

 (Thenea Gray, Sphinctrella Schmidt, PoecilJastra Sollas, Paeh- 

 astrella Schmidt, Nethea Sollas, Triptolemus Sollas, C haracella 

 Sollas) are to be added C helotropaena Lendenfeld (1906, p. 231), and 

 Yodomia Lebwohl (1914, p. 63; Dendy, 1916, p. 232). 



Other genera classed by some in the Theneidae or Paehastrellidae, 

 but in actual fact (namely, without employing phylogenetic inter- 

 pretation) excluded from the combined family as here defined, are: 



Stoeba Sollas (1888, p. 102). Of uncertain position. Assigned by 

 Sollas to the Theneidae, by Dendy (1905) to the Paehastrellidae; 

 merged by Topsent (1902) and Lendenfeld (1903) in Dercitus 

 Gray. 



Dercitus Gray (1867, p. 542). Of uncertain position. Assigned by 

 Sollas (1888), Lendenfeld (1903), Hentschel (1909), and Lebwolil 

 (1914) to the Paehastrellidae; by Topsent (1902) to the Stellet- 

 tidae. 



