18 Transactions of the Society. 



the canals converge. Though now open surface canals, it is likely 

 that they were covered by a dermal layer during the life of the 

 sponge. 



X. Affinities of the Genus. 



The structure of Porosphcera, described above, shows clearly 

 that it is a Calcisponge, belonging to the group of the Lithonina, 

 and its nearest ally is Plectroninia, Hinde,* from Tertiary strata, 

 near Geelong, Australia. In common with the other members of 

 this group, it has a very firm resistant skeletal mesh of fibres 

 composed of four-rayed spicules, each with a partially free apical 

 ray and three facial rays, which are intimately fused with the rays 

 of adjoining spicules. It also possessed a dermal layer of loosely 

 interwoven spicules of a readily destructible character. It is dis- 

 tinguished from Plectroninia by the well-marked simple radiate 

 canals of the interior, by the absence of distinct floors or layers of 

 growth consisting of smaller spicules, not definitely fused together, 

 and further, by the apparent absence of minute " tuning-fork " 

 spicules. From Pctrostroma, D6derlein,f Porosphcera is also dis- 

 tinguished by its radial canals, and its skeletal fibres are not fused 

 into radial balks, with smaller connecting spicules, as in the former 

 genus. Whether the fibres of Porosphcera were invested with a 

 common calcareous pellicle like those of Plectroninia is uncertain, 

 for their state of preservation does not allow of determination. 



XI. Description of Species. 



Porosphcera globularis, Phill. sp. (pi. I., figs. 1-10; pi. II., 



figs. 1-3, 6-10). 



1829. Millepora globularis, Phill., Geol. Yorks., pt. 1, p. 186, pi. i., fig. 12. 

 1833. „ „ S. Woodward, Geol. Norfolk, p. 46, pi. iv., figs. 10-12. 



1814. Ceriopora pisum, Eeuss, Geognostische Skizzen aus Bohmen, vol. ii, 



p. 140. 

 1845. Tragus globularis, Eeuss, Versteinerimgen bolmi. Krei deformation, 



Abth. ii. p. 78, pi. xx., fig. 5. 

 1850. Coscinopora globularis, A. d'Orbigny, Prodr. dePak'ont., vol. ii., p. 284. 

 1854. „ „ Morris, Cat. Brit. Foss., 2nd ed. p. 27. 



1860. Orbitolina globularis, Parker and Jones, Ann. and Mag. Nat. Hist., 



ser. 3, vol. vi., p. 34. 

 1864. Achilleum globosum, F. A. Eoemer, Pateontographica, vol. xiii., p. 56. 

 1875. Coscinopora globularis, Etheridge, Geol. Yorks , 3rd ed. p. 322, pi. i., 



fig. 12. 



1878. Porospjhxra globularis, Steinmann, pars. Pakeontog., vol. xxv.,p. 120. 



1879. Ceriopora nuciformis, Qnenstedt, pars. Petrefactenk. Deutsckf, vol. vi., 



p. 262 ; Atlas, pi. 153, figs. 1-7, 9. 



* Quart. Journ. Geol. Soc, lvi. (1900) pp. 50-66, pis. iii. and iv. 

 t Zool. Jalirb.,x. (1S9S) pp. 15-32, pis. ii.-vi. 



