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Show 570 DR. R. V O N LENDENFELD ON THE SYSTEMATIC [Dec. 21, IV. THE CLASSIFICATION OF SPONGES. Having thus ascertained the systematic position of the Sponges as a group, we now approach the second part of our work. Every one will agree that no satisfactory classificatory system of Sponges exists at present. Spongologists are in the habit of approaching this subject with great caution, I may say with diffidence. It is a remarkable fact that the leading spongologist of the day, my esteemed teacher Prof. F. E. Schulze, in Berlin, has not attempted to work out a classificatory system of Sponges, whilst others have made some desultory efforts in that direction. It is self-evident that the systems established by Bowerbank, O. Schmidt, Gray, and others, which date from a time when virtually nothing was known about Sponges, have now become obsolete. The most successful attempt at establishing a system of Sponges is doubtless that of Vosmaer (1550), who, however, approaches his task with great diffidence ; everywhere we meet in his work with " preliminary " classifications. Some geologists, principally Zittel (1635) and Sollas (1455), have classified the Sponges in a rather high-handed manner, establishing subclasses, orders, &c, without regard to details like families and genera. Zittel particularly attached too much importance to the fossil Sponges. In the groups tbemselves more satisfactory detail work has recently been done. F. E. Schulze (1369) has worked out the Hexactinellids of the 'Challenger' with results which are as valuable and useful as the material at his disposal was abundant and interesting. Zittel (1626-1629) has in a satisfactory manner dealt with the fossil Sponges belonging to the same group. The Lithistids and Tetractinel-lids, both fossil and recent, have been carefully investigated by Zit(el (1639) and Sollas (1453). I (888) have, with the aid of the works of Hackel (627-629) and Polejaeff (1179) at m y disposal, established a system of Calcareous Sponges based on m y investigations of the rich Australian Sponge-fauna, which appears fairly satisfactory. The Monactinellids have been carefully studied by Vosmaer (1545), Ridley (1261), and Ridley and Dendy (1265-1266), and I have myself devoted much labour to their investigation, and have made (870) an attempt at classifying them, which, however, was unsuccessful. The Australian Fauna is exceedingly rich in Monactinellids, and my collection, of over 300 species, has enabled me to work out the classification of some of the groups in detail. No attempt has hitherto been made to classify the Horny Sponges excepting one, contained in a short paper of Vosmaer (1552), establishing five groups, in accordance with the views previously expressed by myself (868), and based on the result of the researches into the structure of horny sponges by F. E. Schulze (1345, 1348, 1349, 1351) and myself (868). The Australian marine fauna is exceedingly rich in horny sponges, so that I have been enabled to work out their relationships in detail. If we review the Sponges as a whole, we shall be struck with the great fundamental difference between the Calcareous and all |