WEAVER: INVERTEBRATE PALEONTOLOGY AND HISTORICAL GEOLOGY 701 



of Ventriculites, which he considered related to the Bryozoa. In 1852 d'Orbigny 

 classified the sponges as Amorphozoaires, dividing them into two orders: (1) 

 Amphozoaires a squelette corne and (2) Amphozoaires a squelette testace. The 

 first order included living forms and the fossils belonging to the genus Cliona; 

 the second order was divided into five families. The finer morphological charac- 

 ters of the skeleton were not considered, and his classification was based largely 

 on external features. E. de Fromentel (1859) in his introduction to the study 

 of fossil sponges — both living and fossil — considered the canal system, pores, 

 osculum, and tubules for classification purposes. Sponges from the Jura Moun- 

 tains were investigated by Etallon in 1859 and 1861, with special attention to 

 the spicules, canal system, and the outer form, all of which he considered of im- 

 portance for classification. Ferdinand Roemer (1860) studied the Silurian 

 sponges of western Tennessee and defined the genera Astylospongia, Palaeoma- 

 non, and Astraeospongia. In 1864 F. A. Roemer published a monograph on 

 the sponges of the North German Cretaceous, with the description of many 

 species and an excellent account of the structure of the skeleton of the Hexac- 

 tinellids and Lithistida. Sponges from the Miocene rocks of Oran were described 

 in 1872 by A. Pomel, who developed a classification consisting of two broad 

 groups, (1) Camptonspongiae and (2) Petrospongiae. The first, with two orders, 

 was characterized by isolated spicules; in the second, with 239 genera, the 

 spicules were arranged in a united framework. Wyville Thompson, who studied 

 the sponges collected by the "Challenger" Expedition, was the first to point out 

 a similarity of structure in the fossil Ventriculites to that in living siliceous 

 sponges. In the last quarter of the nineteenth century considerable advance was 

 made in the study of sponges as the result of the examination of thin sections 

 under the microscope. By this method SoUas in 1877 compared several genera 

 from the English Chalk with living hexactinellids and monactinellids. Similar 

 studies by von Zittel (1877-1878) led him to consider that all sponges, both fos- 

 sil and living, should be included in a single classification. Hinde, in the light 

 of increasing knowledge of the morphology, presented a classification very close 

 to that now in general use. It included the four orders Myxospongia, Cerato- 

 spongia, Silicispongia, and Calcispongia. A discussion of the advances made in 

 the investigation of fossil and Recent sponges, along with a more advanced 

 scheme of classification was given in a monograph by Rauff in 1893-1894. This 

 grouping is used in the translation by Eastman (1913) of von Zittel's Inverte- 

 hrate Paleontology, in which the sponges are placed in the phylum Coelenterata 

 along with the corals but are included in the subphylum Porifera and in the class 

 Spongiae. The four subclasses Myxospongiae, Ceratospongiae, Silicispongiae, 

 and Calcispongiae are still recognized but the first two, because of their lack of 

 imperishable hard parts, are not included in the textbook. The Silicispongiae 

 are divided into four orders, the last two of which include the majority of fossil 

 sponges. The Calcispongiae include two orders, Pharetrones and Sycones. The 

 classification is based largely on differences in the character of spicules, whether 

 single or united into a framework, thickness of walls, character of pores and 

 tubes, and the osculum. 



Monographs dealing with special groups of sponges have contributed greatly 

 to the advances made during the past sixty years. Among the more important of 

 t;hese is the work on the Dictyospongiae-Paleozoic Reticulate Sponges, which was 



