24 ART. 1. 1. TJIMA : IIEXACTTXELLIDA, ITI. 



'Now as to the division of the Euplectellidœ into subfamilies. 

 Of these, three have been recognized by F. E. Schulze ('99, p. 

 97), viz., the Holascinœ, the EnplectelHnir and theTœgerina'. 



The Hexasterophora, it seems safe to say, should have had for its prototype a form 

 which was firmly attached by its base to the hard substratum. Whenever a Ilexactinellid 

 is thus tixedly seated, even though it be a s^o-called Lyssacina, it is quite generally true 

 that certain small liexactinic spicules occurring at the base very early undergo fusion, 

 beginning with those in direct contact with the substratum, thus bringing about a typically 

 dictyonine framework at tlie part. This miglit luive taken origin in consequence of the 

 sponge requiring a certain degree of firmness at the part of attachment. That rigid frame- 

 work, so far as it occurs in lyssacine Hexactinellids, I have called tlie hanidiclj/nnalia 

 (Contrib. I., pp. 186 [foot-note], 232 and 264). The same framework it is, I liold, which 

 has reached the most extensive development in the so-railed Dictyonina and lias been 

 called by F. E. Schulze the dirlyonalia. Tlie basidictyonalia and the dictyonalia I consider 

 as genetically and morphologically identical. Botli retain a primitive character in that 

 they alike consist, as a general rule, of hexactins only, although derivative forms of 

 spicules with a smaller number of rays may secondarily come into fusion witli the beams. 

 The true dictyonine skeleton as here specified, should be kept distinct from another kind 

 of ankylosed framework in wliich the elements involved are not solely hexactins, but 

 principally derivatives of tlie sime, such as stauractins, tauactins, diactins, etc. (as, e. g. in 

 the rigid skeletal frame of the lateral wall or the stalk in the EupIectelUmr). The rigidity 

 in the latter case is clearly a much later acquisition than that in the basidictyonalia or 

 the dictyonalia. For, before the ankylosing process, starting at the base, has encroached 

 upon the parts occupied by the derivative spicules indicated, these must have had a long 

 period of loose existence during which they should have derived their^shnpe from the 

 original hexactinic form,— which would be impossible had they been soldered together 

 l)eforehand. From this standpoint, the well-known skeletal framework of f. i. Eiiplectella 

 aapei-giUum, notwithstanding the completely ankylosed state of its component spicules, ought 

 not to be confounded with the basidictyonalia or the dictyonalia of certain other Hex- 

 actinellids but should fill under the lyssacine category, in which the ankylosis has but 

 secondarily set in. 



But to return to the Hexasterophora prototype. I consider this to have already 

 possessed at its base a basidictyonal mass in addition to the loose spicules of the body 

 proper, which were directly inherited from the Hexactinellid ancestor. In other words, it 

 may be said that the skeleton was partly dictyonine and partly lyssacine in character,— a 

 dual condition, which, in general, may be said to obtain in all the recent Hexasterophora, 

 if we except those forms which have apparently lost the basidictyonalia in secondarily 

 adapting themselves to the special mode of attachment by means of anchoring spicules 

 (Euplectellinîe, Lophocalyx, Mdonympha). During the phylogeny, the elements of the dictyo- 

 nine portion have remained essentially unchanged in character, as they should owing to 

 their rigidly fixed state. On the other hand, those of the lyssacine portion have been 

 capable of adapting themselves in manifold ways to varied conditions of existence, analo- 

 gously to the similarly circumstanced spicules of the Amphidiscophnra, the result being the 

 multifarious hexactin-modifications— amongst them the h?xasters— which we meet with in 

 the Hexasterophora. 



