REPORT ON THE HEXACTINELLIDA. 109 



terminal umbel, from the lateral margin of which about sixteen pointed teeth project. It 

 is remarkable that these hemispherical or globular terminal umbels are not of equal size, 

 the central having but about half the diameter of the four surrounding it (PI. XII. 

 fig. 11). 



In a fragment of this species which Professor Oscar Schmidt had kindly placed 

 at my disposal, I found a few other rosette forms, namely, first, oxyhexasters with two 

 diverging thin terminal rays on a very short principal (PI. XII. fig. 9), just like those so 

 frequent in diff"erent species of Euplectelln, and secondly, small discohexacts in which 

 upon the outer extremities of every simple c3dindrical principal ray, a hemispherical 

 hollow terminal disc with marginal prongs was so adjusted that the cavity seemed to 

 be directed not inwards but outwards. 



The stars which Oscar Schmidt observed in Rhahdopectdla tintinnus, and which he 

 compared to the Tethya-stavs, I have likewise seen, and have figured them in PI. XII. 

 fig. 12. I regard them as oxyhexasters in which the strong terminal rays have at their 

 base grown together laterally on the very shoi't principal rays. 



Finally the rough bow-shaped spicules (PI. XII. fig. 10) deserve to be mentioned. 

 The great resemblance between these forms and those of Euplectella jovis has already 

 been noted by Oscar Schmidt. 



Genus 6. Hertwigia, 0. Schmidt. 

 This genus includes only the single species mentioned below. 



Hertwigia falcif era, 0. Schmidt. 



From a knotted and branched basis, according to Oscar Schmidt's representation, 

 there arises an irregular labyrinth of tulx'S with thin leaf-like walls, supported l>y 

 a lattice-like framework of obliquely crossed rods and fibres. Owing to the defective 

 preservation of the upper much damaged portion it was not possible to frame any 

 satisfactory conception of the whole form. Among the looser siliceous spicules, Oscar 

 Schmidt mentions — (l) hexradiate spicules and derivative five- and three-rayed forms, 

 which are for the most part rough towards the point, while others exhibit a fir-tree-like 

 ray with at most very short prickles ; (2) rosettes with four intersecting umbel teeth ; 



(3) rosettes with larger teeth on the backwardly bent margin of the terminal umbel ; 



(4) the " specific Euplectella rosettes," that is to say, floricomes ; and (5) two kinds of 

 sickle-rosettes, one of which carries on the hemispherical terminal disc of each principal 

 ray several whorls of sickle-like terminal rays, while in the other four large sickle-like 

 teeth are inserted on every principal ray. Kods with numerous oblique lateral prickles 

 at one end are sc, ttered here and there. Oscar Schmidt also mentions delicate 



