KEPORT ON THE KERATOSA. 81 



Spongelidse from the Chalinidse ? Indeed, the most simple procedure is to adopt the 

 Keratosa as an independent group ; but it should not be overlooked that this procedure 

 is nothing more than the concession to our natural wish to have for the groups we 

 establish the sharpest possible diagnoses. 



I should like to summarise my conclusions. We have seen that the subdivision of 

 the Keratosa into two orders is inadmissible ; we have seen that their subdivision 

 directly into families gives also as results families of a very ambiguous nature. After the 

 above deduction we can but say that all this is very comprehensible, since the ivhole 

 group is nothing more than a simple family. Of course, as is the case with the 

 suljtype of Acrania, a high systematic subdivision can be represented by a simple 

 family; and, on the other hand, as is the case with, e.g., Terebellidae, a family can be 

 subdivided into numerous subfamilies, these latter consisting again of generic unities. 

 This latter measure finds, however, its application in exceptionally rare cases, and only 

 then when it is really necessitated by the richness of the forms as well as by the richness 

 of systematic characters, and, on the other hand, by higher phylogenetic considerations, 

 while the immediate purpose of my foregoing discussion consisted precisely in the attempt 

 to prove that it is due exactly to the erroneous opinion that Keratosa forms a systemati- 

 cally high subdivision, that natviralists split them into orders, suborders, and families. 

 Of course, it cannot be denied that certain genera established in them are more closely 

 connected one with another than with the remaining representatives of the group. This 

 would be, however, only of consequence if all the genera in question were homo- 

 geneous, while in reality some of them are undoubted genera, the others perhaps but 

 species. This is the gist of the matter, and I think that the only natural reconciliation of 

 all these contradictions can be obtained by rendering our genera equivalent one to 

 another, which can be realised by enlarging the idea of genus, e.g., by uniting forms, 

 distinguished as Hippospongia, Euspongia, &c. , in the single genus Spongia, which would 

 be, on the whole, thoroughly equivalent to the genus lanthella or Darwinella. But if the 

 species constituting the conjectural genera Hippospongia or Stelospongos are yet undoubted 

 species 1 I answer, prove that they are so, and in that case subdivide the genus Spongia 

 into corresponding subgenera. As is well known, these latter systematic unities are out 

 of use ; I regai'd, however, their introduction in systematic practice to be equally profit- 

 able for systematic purposes in general, as well as with respect to the special case of 

 classifying the Keratosa in a tolerably natural manner. I opened my " criticism of the 

 genera " with a comparison of different opinions as to the value of generic distinctions, 

 and we have seen that in this respect diametrically opposite ideas have been expressed by 

 different naturalists. The word "diametrically" just used alludes to the impossibility 

 of their thorough reconciliation; the introduction of subgenera in zoological calcula- 

 tions would reconcile them at least so far as this is possible, and again it is obvious 

 that sooner or later this reconciliation must be realised, since neither the opinions of Nageli 



(ZOOL. CHALL. EXP. — PART XXXI. — 1884.) Hll 11 



