162 Prof. W. J. Sollas on the 



he shows that they exist. Vosmaer *, falling into the old 

 snare of classifying from a single character, exclaimed against 

 my placing D. ijhnum along with Schmidt's forms, on the 

 ground that it possesses anchorates, which the latter were not 

 supposed to possess by Schmidt. I have no doubt that, on 

 second thoughts, this able investigator will admit that the 

 assemblage of characters is after all of greater importance 

 than a single one, 



Clas.'ii/ication. — Tetilla is a genuine though somewhat 

 divergent member of the corticate Choristidge, with close 

 affinities to the Desmacidina ; it links together the suborders 

 Tetractinellida and Monaxinellida. The evidence for this 

 statement is found first in its embryological development, next 

 in the characters of the Esperiad Rhaphidotheca Marshnll- 

 HalJi, Kent. In the embryo we find som.e of its tetractinellid 

 spicules in course of development ; they commence witli a 

 swelling at the distal end of large uniaxial spicules, from 

 which afterwards teeth are budded oif one by one. Tiiis is 

 true both for the grapnel- and fork-shaped spicules. Thus 

 the uniaxial clearly precedes the tetractinellid form in deve- 

 lopment, a fact of signal imjiortance in the discussion els to 

 which originated first, Monaxinellida or Tetractinellida, 

 and in complete correspondence with observations made on 

 the order of development of the spicules in the Calcispongia^. 



In the next place, in Rhajiliidotheca Marsliall- Halli we find 

 the distal ends of some of the large spicules Avhich project from 

 the skeletal fibres beyond the skin distinctly thickened into 

 globular or oval or cylindrical bulbs, in which the axial 

 thread ends in a slight spherical expansion. To suppose that 

 these spicules are parasitic in nature or foreign bodies appro- 

 priated by the sponge is an altogether untenable idea, as 1 shall 

 show when dealing more in detail with this species ; they 

 agree in all respects with the other chief spicules of the 

 sponge, except in this one important particular, that they have 

 a dilated or thickened distal end, and thus maintain persis- 

 tently, though in an exaggerated form, a stage through which 

 tlie trifid spicules of Tetilla very rapidly pass. The rounded 

 swelling of tiie distal ends of projecting spicules is not confined 

 to lihcvpliidotheca ; I have it in a less marked form in a suberite 

 to which I give the name of Radiella sclicenus {a^oivo<;j a bull- 

 rush) . 



In the next place, amongst the various forms of small 

 spicules with which Rhcq^Mdotheca is richly provided, we find 

 trichite sheaves and C- and S-shaped hamates. The pre- 



* ' The Spouges of the Leyden JMuseuni/ by G. C. J. Vosmaer. Family 

 Desmacidina}, p. ].^4. 



