276 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



Dendy, 1905) ; Corticella Sollas, 1888 (merged by Lendenfeld, 1903. 

 in Colthropella Sollas, 1888) ; Rhacella Sollas, 1888 (merged by Len- 

 denfeld, 1903, in Plakino). 



Family 3. Thrombidae. The only genus is Thrombus Sollas, 

 1888. Lendenfeld, 1903, transfers the genus to the Plakinidae, 

 deleting Thrombidae. 



(For the definitions and contents of the remaining groups which 

 are given by name below, see the text.) 



Suborder 2. Astrophora Sollas, 1888. 



Suborder 3. Hadromerina Topsent, 1898. (Hadromerina Topsent, 

 1898c, plus Chondrosidae ; Pseudotetraxonina Vosmaer, 1887, plus 

 Clavulina Vosmaer, 1887, plus Oligosilicina part Vosmaer, 1887, 

 plus; Clavulina Vosmaer, Ridley and Dendy, 1887, plus; Spintharo- 

 phora Sollas, 1888, minus Axinellidae plus Epipolasidae Sollas. 

 1888, plus Placospongidae Sollas, 1888, plus; Astromonaxonellida 

 Dendy, 1905.) 



Suborder 4. Sigmatophora, Sollas, 1888. 



Suborder 5. Halichondrina Vosmaer, 1887 (Halichondrina Au- 

 thors, Sigmatomonaxonellida Dendy, 1905.) 



Suborder 6. Lithistida O. Schmidt, 1870. 



Order 4. Keratosa Grant, 1826, 1861. 



A close linkage of the Astrophora and Hadromerina on the one 

 hand, under the designation Astrotetraxonida (Hentschel, 1909), 

 and of the Sigmatophora and Halichondrina on the other, under the 

 designation Sigmatotetraxonida (Hentschel, 1911a), has come into 

 extensive use in recent years (Dendy, Hentschel, and others; also 

 the Zoological Record). It has not been, however, by any means 

 universally adopted (see Topsent, Thiele), and I am now inclined 

 to believe that it rests on too many assumptions. And yet it is gen- 

 erally recognized that many of the Hadromerina give indication of 

 their descent from the Astrophora, the relationship between the two 

 being fully as close as, if not closer than, that between the Astro- 

 phora and Sigmatophora. This makes somewhat artificial the main- 

 tenance of the older groups Tetractinellida, comprising the 

 Astrophora and Sigmatophora. and Monaxonida, comprising the 

 Hadromerina and Halichondrina, for we are very much in the dark 

 as to the genetic relationship between the two latter subdivisions. 

 Under these circumstances recourse may be had to the noncommittal 

 method of arranging the subgroups (Astrophora, Hadromerina. 

 Sigmatophora, Halichrondina) serially, and this to-day seems to me 

 •"he best practice. 



The collection is deposited in the United States National Museum. 



Since the manuscript of this report was completed, several memoirs 

 of importance have appeared, bul the writer believes that the data 

 in them, however valuable, do not necessitate changes in the views 

 on classification here adopted. 



