2 Transactions of the Society. 



competent authorities have questioned his conclusions. The general 

 resemblance of Porosphcera to sponges, which has led several 

 authors to place the fossils in this group, induced me for many- 

 years past to collect and study all the forms I could meet with ; 

 for a long time I failed to discover any decisive evidence respect- 

 ing the original characters of their calcareous skeletal fibres, but 

 at last, about eight years ago, a small specimen, preserved in flint, 

 which was sent to me by Mr. H. Muller of Eltham, clearly showed 

 that the fibres were built up of spicules. On further investiga- 

 tion this spicular structure was recognised in microscopic sections 

 of many other specimens, and it became apparent, as I have already 

 mentioned elsewhere,* that Porosphcera belonged to the Lithonine 

 division of Calcisponges, and possessed the same structural cha- 

 racters as the genus Plcctroninia, Hinde,f from the Eocene Tertiary 

 of Victoria, Australia, and the recent Pctrostroma, D6derlein,| from 

 the Japanese sea. 



Other work has prevented me from giving till now a detailed 

 description of the structure of Porosphcera, but the delay has 

 been in one respect an advantage, for in the interval my friend, 

 Dr. A. W. Howe, F.G.S., has carried on a series of researches on 

 the fossils from the different zones of the Chalk on the east and 

 south coasts of England, during which he has met with many 

 hundred examples of Porosphcera, all of which he has most 

 generously forwarded to me for examination. The study of this 

 large series of well-preserved specimens, together with those of 

 my own collecting, has enabled me to gain a better knowledge of 

 the real characters of these fossils than hitherto, and, further, to 

 trace out their distribution in the various zones of the Chalk of 

 this country. 



II. History of the Genus. 



The following is a brief history of the fossils which are now 

 included under Porosphcera. 



In 1822, Dr. G. A. Mantell figured, in the Geology of Sussex, 

 pi. xvi. figs. 17, 18, p. 162, ' Siliceous specimens of a Zoophyte of 

 a pyriform shape, the nature of which is unknown,' from the 

 Chalk near Brighton. These are examples of Porosphcera nuci- 

 formis, von Hag. sp. Eigs. 22-24 of the same plate, referred to 

 Lunulites (?), probably belong to P. patettiformis. In 1835, they 

 were placed by this author under Orbitolites Icnticulata, Lam., 

 Trans. Geol. Soc. s. 2, vol. iii. p. 204. 



In 1829, Prof. J. Phillips, in the Geology of Yorkshire, pt. i. 

 p. 186, pi. i., fig. 12, gave a figure of Millepora globularis, and 



• Quart. Journ. Geol. Soc, lvi. (1000) p. 57. t Op. cit., p. 51. 



% Zool. Jahrb., x. (1898) pp. 15-32, pis. ii.-vi. 



