124 COELENTERATA— HYDROZOA phylum ii 



Idiostroma Winch. Coenosteum cylindrical or fasciculate, traversed by 

 axial, tabulate zooidal tubes, which give off secondary lateral tubes. General 

 tissue reticulated, similar to Stromatopora. Devonian. 



Labechia E. and H. Ordovician and Silurian ; North America and Europe. 



Stylodidyon, Sfromafoporella and Syringostroma Nich. ; Amphipora Schulze ; 

 Stachyodes Bargat. Devonian of Europe and North America. 



A number of genera are described by Waagen and Wentzel from the 

 Permo-Carboniferous rocks of Farther India, such as Carterina, Disjectopora, 

 Circopora, etc. Probably in the same neighbourhood should be placed several 

 peculiar encrusting marine forms from the Carboniferous of Belgium, described 

 by Glirich under the names of Aphrostroma, Spongiostroma, Chondrostroma, 

 Malacostroma, etc. The first-named of these occurs also in the Silurian of 

 Gotland, and was associated by Giirich with the Foraminifera. 



Order 4. CAMPANULARIAE Allman. 



(Leptomedusae, Calypioblastea Allman ; Thecaphora Hincks). 



Delicate, branching, plant-like, sessile colonies, with chitinous periderm, enveloping 

 the base, pieduncle, and also the cup -like receptacles {Jiydrothecae) which enclose the 

 individual polyps. The proliferous zooids are developed within urn-shaped capsules 

 (gonothecae) of comparaiively large size, and sometimes become separated off as free- 

 swimming velate Medusae. 



Recent Campanularians, such as are comprised by the families Sertularidae, 

 Plumularidae and Campanularidae possess durable hard parts, but nevertheless 

 their remains have not as yet been found in the fossil state, with the exception 

 of a few forms from Pleistocene deposits. 



Range and Distribution of the Hydromedusae. 



Of those members of this group in which the preservation of structural 

 parts is at all possible, the Hydrocorallinae have been recognised with 

 certainty as early as the Upper Cretaceous. During the Tertiary they 

 became more widely distributed, and at the present day are important reef- 

 builders. 



During the Upper Jura, and notably in Tithonian beds of the Mediter- 

 ranean region, certain genera of the Hydractinidae {Ellipsactinia, Sphaeractinia) 

 are abundantly represented. Contrariwise, other Tubularians, such as the 

 Triassic Ileterastridium, and Farkeria and Porosphaera from the Cretaceous of 

 central I^urope, occur only sparsely. 



The extinct organisms known as Stromatoporoids were extremely 

 important rock-builders during the Paleozoic, much of the limestone of the 

 Silurian and Devonian systems resulting from the destruction of the reefs 

 built by these fossils. Their massive stocks sometimes attain gigantic size. 

 Stromatoporoid remains are profusely distributed in Ordovician and Silurian 

 rocks of North America, England and Russia, also in the Middle Devonian of 

 the Eifel and Ardennes, and in equivalent strata of Nassau, Devonshire, the 

 Urals, Spain, etc. Except for a few rare survivors, the group does not 

 continue beyond the Paleozoic era. 



