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



me, the t5''pical union of the dictyonalia is wholly absent, although no one has any doubt 

 that AphrocaUistes, in the general structure of its skeleton, and especially in the 

 structure and disposition of its isolated spicules, belongs to the Dictyonina, and is to 

 be referred to the neighbourhood of Euretidse and Coscinoporidse. As an instance of the 

 second case, where a skeleton which is macroscopically like many dictyonal frameworks 

 contains only isolated examples of two hexradiate spicules uniting in the typical fashion, 

 I may refer to Euryplegma auriculare. 



In regard to this form I have indeed hesitated for a long time whether I should refer 

 it to the Lyssacina or to the Dictyonina. At first, in my memoir Ueber den Bau und 

 das System der HexactineUiden,^ I regarded it as a Dictyonine, but have finally preferred 

 to place it among the Lyssacina, and beside the Rossellida^, which, both in regard to the 

 structure of the loose needles and the absence of uncinates, it resembles more closely 

 than it could any Dictyonine form. In its other characters it is, however, Dictyonine- 

 like, though the absence of uncinates and scopulse give it a peculiar appearance and must 

 always make its position exceptional. 



It was a fact of much interest to me that my respected colleague Professor 

 Zittel unhesitatingly referred a macerated skeleton of Euryplegma, which I asked him to 

 examine in the Berlin Zoological Institute, to the Dictyoninal type, while allowing that 

 various microscopical sections of the same skeleton comj^letely resembled the Lyssacina 

 in the spicular union of the framework. 



There are, indeed, other distinctive characters between Lyssacina and Dictyonina 

 than the mode of union of the spicules, but these also establish, not a fundamental 

 separation, but only a difierence of degree. Previous investigators have noted the readily 

 verified fact that in all emphatically Lyssacine types, which form a connected skeletal 

 framework, there occurs, besides the simple soldering of the spicule branches, another 

 very frequent mode of union by means of short connecting bridges, the so-called 

 sjmapticula, which bind together more or less approximated rays of adjacent spicules, 

 which are not, however, in actual contact. By the development of numerous synapticula 

 at approximately uniform intervals, there arises a scalariform structure, which is regarded 

 by some as characteristic of the Lyssacina with connected framework, and as contrasting 

 them with the Dictyonina. But while it is indisputable that such scalariform structures 

 occur with great frequency, indeed quite regularly in the framework of Lj^ssacina, it is 

 incorrect to assume that they are absent from all Dictyonina. I have observed them, 

 though not frequently, yet quite typically developed in indisputable Dictyonina, such as 

 Fieldingia lagettoides, S. Kent, which in its uncinates and scopulse is certainly one of the 

 Dictyonine series. 



Another fact, to which I first called attention, is the early union of the dictyonalia 

 simultaneously with the development of the associated portion of the body, which is, so 



1 Ahhandl. Kiiiiigl. Preuss. Akad., 1886. 



