CXXXIV 
THE VOYAGE OF H.M.S. CHALLENGER. 
Phylogeny of the Streptastrosa. 
Theneidae PachastrellidsB 
Dercitus Calthropella 
Pachastrella 
Characella 
Thenea Spliincirella Poecillastm 
I 
Stoeba 1 Placinastrella ? Triptolemus 
Nethea ? 
In this scheme Poecillastra is doubtfully supposed to have originated from Thenea- 
like Sponges, which may have been nearly allied to Sphinctrella, some of the species of 
which are incrusting and others not, but none possess dichotrisenes like those of Thenea. 
Nethea and Stoeba are supposed on account of their burrowing habits to be degenerate 
forms. 
As an alternative scheme for the Theneidae the following may be suggested : — 
Thenea 
Sphinctrella Characella 
1 I 
.1 
PachastrelUdx Poecillastra Triptolemus 
Placinastrella 
Demus II. Euastrosa, Sollas. 
Euastrosa, Sollas, Encyclopaedia Britannica, vol. xxii. p. 423, 1887. 
Astrophora in which euasters are always present, but never spirasters nor sterrasters. 
Trisenes are present but not calthrops. 
Family I. Stellettida:. 
Group Stellettina, Carter, Ann. and Mag. Nat. Hist., ser, 4, vol. xvi. pp. 48, 67, 81, 1875. 
History. — The central type of this family is the genus Stelletta, which was originally 
defined by 0. Schmidt in 1862 ^ and at that time placed by him amongst the so-called 
^ 0. Schmidt, Spong. Adriat. Meeres, p. 46, 1862. 
