1904.] SPOXGES OF THE GENUS LEUCOSOLENIA. 353 



the inonaxons, and, as sliowii by Bowerbank's figures, a great 

 tendency to the pi-oduction of abnormal forms of triradiates (see 

 text-fig. 95, figg. 18a-e and 19 a-h, p. 379). Leuconia somesii 

 may, in short, be characterised as an interesting aquarium variety 

 of LeuGosohnia variabilis, showing modifications parallel to those 

 described by Bidder for Sycon raphanus *. growing in the Naples 

 Aquarium. Bowerbank himself was struck by the resemblance of 

 this sponge to a Leucosolenia, and particulai-ly to the specimen 

 figured by him in pi. iii. fig. 1, which, as stated above, was 

 actually a specimen of L. variabilis ; he remarks that the only 

 other known British calcareous sponge with which this species is 

 likely to be confounded is Leucosolenia botryoides, but " only in 

 its young and immature state." Leuconia somesii must therefore 

 be put as a synonym of Haeckel's species variabilis. 



Enough has been said to justify the criticism made above that 

 Bowerbank did not grasp the real distinctions between the species 

 of his genus Leucosolenia t. It is the great merit of Haeckel, 

 whose name marks the next epoch J in our knowledge of calcareous 

 sponges, that he was the first to understand the great importance 

 of the spicules in specific determinations, and to give descriptions 

 of the species by which they could be recognised clearly. It 

 may be said, in short, that previous to Haeckel's great mono- 

 graph no species of calcareous sponge was reallj^ adequately 

 characterised, and that Haeckel was the first to show how this 

 should be done. Hence, where previous descriptions of a cal- 

 careous sponge leave us in doubt as to its identity, Haechel's 

 determination of its characters fixes the ajyplication of the name. 



Had Haeckel carried out his own method with accuracy and 

 conscientiousness it would not have been necessary for the present 

 paper to be written, but unfortunately this is far from being the 

 case. Of the specimens which I have been able to examine, 

 some have been through Haeckel's hands and have been identified 

 by him, and these show, in many cases, the most extraordinary 

 errors of identification, as will be evident from the descriptions 

 and figures given below. It will be made clear, also, that in tv{o 

 cases at least he fovmded unnecessary species simply as the result 

 of overlooking spicules in certain specimens which he found to 

 be present in others of the same species. Haeckel's numerous 

 species of Ascons require, one and all, a thorough re-examination, 

 and there can be no doubt that a careful revision would result in 



* Quart. Journ. Micr. Sci. v. xxxviii. p. 10. 



t To the well-known monograplis of Oscar Schmidt [19, 20], more or less con- 

 temporary with Bowerbank's writings, further reference is not necessarj' here, since 

 of Leucosolenia, in the sense used in the present memoir, only two species are 

 described, X. lieherJcvhnii, which is not a British form, and JL. fabricii, which 

 appears to be a synonym of compUcata. 



X Both of Haeckel's works, the ' Prodromus ' (1870) and the ' Monographie ' 

 (1872), were published at dates between those of the second and third volumes of 

 Bowerbank's ' British Spongiadaj ; ' but they were not noticed by Bowerbank, and 

 belong in all respects to a subsequent epoch. Of Bowerbank's species, onlj- Leuconia 

 somesii was described after Haeckel's monograph, and is therefore not noticed by the 

 latter. 



Proc. Zool. Soc— 1904, Vol. II. Ko. XXIII. 23 



