558 Notices of Memoirs — The British Association. ■ 



P. Whitfield published observations on the structure of Dictyophjton 

 and its affinities with certain sponges, accompanied by a note from 

 Dr. J. W. Dawson, on the structure of a specimen of Uphantoenia, 

 etc. (D. Walcott on the Nature of Cyathophjciis.) 



In the same year E. P. Whitfield (with note by Dr. J. W. Dawson) 

 described two species of Dictyophjton and one of Uphantcenia. 

 (Bulletin of the American Museum of Natural History.) 



In 1882, James Hall upon Dictyophyton, Phragmodictya, and 

 similar forms with Uphantoenia. (American Association for the Ad- 

 vancement of Science.) 



In the European literature, the first notice of which was observed 

 by the writer, of any fossil resembling Dictyophyton, is in 

 Murchison's Silurian System (1839), where Cophinus dubius is 

 described and figured. 



(In Morris' Catalogue this fossil is placed in the category of incerice 

 sedes.) 



In 1845, M'Coy, in his 'Synopsis of British Palgeozoic Fossils,' 

 describes Tetragonis Danhiji (Receptaculites Danhyi, Salter in MS.). 



In 1874 Mr. Salter, in his Catalogue of the Cambrian and Silurian 

 Fossils in the Cambridge Museum (p. 176), places Tetragonis Danbyi 

 under the Spongidse. In 1880, Dr. Ferdinand Eoemer has described 

 the genera Dictyophyton and Uphantoenia (Lethea geog. Thiel, p. 

 126 and 128), placing them among the Algee. At a later date the 

 same author places Tetragonis Murchisoni, T. Danbyi, and T. Eifelensis 

 among the Spongidje. 



In 1883 the same author (' Zeitschrift der Deutschen Geologischen 

 Gesellschaft,' Bd. xxxv. p. 704) has discussed the relations of Tetra- 

 gonis Eifelensis, with Dictyophyton, describing and illustrating Dictyo- 

 phyton Gerolsteinensis. 



This group presents a great variety of form in the mode of growth. 

 The structure of the frond which characterizes every member of this 

 family, may be described as a reticulation of tubular spicules forming 

 rectangular meshes. In the simpler forms these meshes alternate in 

 size and strength, owing to the regular alternation in the size of the 

 bundles of spicules which determine the meshes. In the prismatic 

 and nodose forms, certain bundles of spicules become very much 

 developed and produce the characteristic form and ornamentation of 

 the cup. The middle layer is uniformly reticulate ; while the inner 

 and superficial layers show an oblique and sometimes a radiate 

 arrangement of spicules. In the highly-ornamented species the 

 outside layer of spicules is often produced into tufts, spines, and 

 intersecting fimbria or lamina of greater or less prominence. 



In the foreign literature accessible to the writer there are six 

 species of this family described. In preparing a memoir on the 

 subject he has been able to recognize, from personal examination, 

 thirty-seven American forms, the oldest geologically being from the 

 Utica State, and the latest form from the Keokuk limestone of the 

 Carboniferous system. These thirty-seven species have been de- 

 scribed under the following genera, viz. : Cyathophycus Walcott, 

 Dictyophyton, Ectenadictya, Lyrodictya, and Fhysospongia, Hall ; and 

 TJphantonnia, Yanuxem. 



