The Genus Porosphcera, Steinmami. By George J. Hinde. 5 



author's Grunchugc der Palceontologie (1895) p. 102, it is placed 

 next to Parker ia iu the Order Tubularia3 ; and in the English 

 edition of the work (1900) p. Ill, it is retained in the same 

 position. 



Treating of the affinities of the genus Parkeria, Carpenter, 

 Ann. and Mag. Nat. Hist., s. 6, vol. i. (1888) p. 11, the late Prof. 

 H. A. Nicholson stated that microscopic sections of Porosphcera 

 globidaris show that its minute structure differs from that of any 

 Hydrozobn, and that it has no special relationship with Parkeria. 

 The author thinks that it will be found to belong to the group of 

 the Lithistid sponges, and to be related to the genus Hinclia, 

 Duncan. The same opinion is also expressed in the Manual of 

 Palccontology, 3rd ed. (1889) vol. i., p. 200. 



Prof. A. Fritsch. gives a description of Amorphospongia globosa, 

 v. Hag. sp., in Studien im Gcbicte der bohmische Kreidcformation, 

 iv. Die Teplitzer Schichten (1889) p. 108, fig. 52. It is stated 

 that the inner skeleton appears to consist of a plait-work of cal- 

 careous spicules, and that there is a surface layer which likewise 

 seems to be of spicules. Through the kindness of Dr. Fritsch, 

 I have examined a microscopic section of the specimen which he 

 has described, and can confirm his statement of the spicular 

 character of the interior skeleton, which is similar to that of 

 Porosphccra globular is ; but I failed to recognise any spicular struc- 

 ture in the outer crust. The specimen seems to me to belong to 

 P. globidaris, Phill. 



G. J. Hinde stated in the Quart. Joum. Gcol. Soe., vol. lvi., 

 Feb. 1900, p. 57, that Porosphccra, Steinmann was a Calcisponge in 

 which the spicules of the skeletal mesh were fused together as 

 in Plcetroninia and Petrosiroma, and that it belonged to the 

 Lithonina. 



Dr. Gr. Steinmann, in the Einfuhrung in die Palaontologie (1903) 

 p. 95, places Porosphccra globularis in the Lithonina as a group 

 of the Pharetrones. 



The varied opinions respecting the nature of Porosphccra indi- 

 cated in the references given above may to some extent be 

 accounted for by the minute and delicate structure of the fibrous 

 skeletal mesh of the organism, which appears in the majority of 

 microscopic sections, even of well-preserved specimens, as a con- 

 tinuous network in which scarcely any traces of the constituent 

 spicular elements can be recognised. Another source of error 

 arises from the fact that certain zones of the Chalk in which 

 Porosphccra is plentiful likewise contain specimens of the siliceous 

 sponge, Plinthosella squamosa, v. Zitt., which closely resemble 

 Porosphccra globidaris in form and size, and the two kinds of 

 sponges appear to have been confused together by von Hagenow 

 and other authorities. 



