332 THE VOYAGE OF H.M.S. CHALLENGER. 



Geuus 3. Cyrtavlon, F. E. Schulze (PI. XCIL). 



Volvulina,^ 0. Schmidt. 



1880. O. Schmidt, Spongien des Meerbusens von Mexico, p. 58. 



History. — Among the sponges of the Gulf of Mexico, Oscar Schmidt^ found some 

 He.xactinellida of cylindrical, globular, or beaker-like form, which were procured from 

 Morrolight, Barbados, and St. Vincent, from a depth varying from 100 to 300 fathoms. 

 These he has embraced under the specific name of Volvulina sigsheei. Their 

 siliceous networks are united in an irregular lattice-work by strands, varying from ^ to 3 

 mm. in thickness. Between these strands there are pores and passages, the outer 

 openings of which appear to be covered by a membrane. A true gastral cavity was 

 not observed, but, on the other hand, a pitting here and there was regarded as 

 pseudogaMral. 



The dictyonal framework exhibits knobbed and also smooth beams. These unite in 

 some species in round tubercled nodes of intersection, while thickenings of this kind 

 are entirely absent at the intersections in other species. 



In the outer skin hexacts or pentacts occur, and these are arranged in a regular 

 network. Moreover, among free spicules there are (l) slender thorny spicules (uncinates), 

 which, in the specimens procured from St. Vincent, always exhibited a central 

 circular swelling; (2) club-shaped brooms (scopula3) ; (3) hexacts with large finely- 

 toothed hooks on the ends of the rays ; (4) umbel-like rosettes (discohexasters), the 

 single ray in each of which is prolonged without forking, and terminates in a point, but with 

 a little thickening before the extremity. 



In the fragment figured in PL XCIL fig. 9, which was very kindly intrusted to me by 

 Professor Oscar Schmidt for comparative examination, I was able to corroborate his 

 important remarks on the striking want of uniformity in the dictyonal framework. I 

 find on the outer surface greatly thickened beams, which are richly beset with large wart- 

 like knobs ; in the interior of the framework the beams in some places are ornamented 

 merely with small pointed knobs, while in others, on the contrary, they are quite smooth. 

 While in some species densely tuberculate nodes of intersection are present, these are 

 completely absent in others. 



I have indicated above the general characters which may be inferred from the 

 specific features noted 1)y Oscar Schmidt, but the generic diagnosis of Volvulina, in 

 contrast to that of some allied genera, may be formulated in the following manner : — 



Cyrtaulon, F. E. Schulze (= Volvulina, 0. Schmidt). 



Cylindrical, conical, or beaker-shaped forms, in which the dictyonal framework con- 



' The name " Volvulina^' has been applied to a Gasteropod since 1865. 

 '^ O. Scliniidt, Spongien des Meerbusens von Mexico, p. 58, 1880. 



