194 CALCAEEOUS SPONGES. 



new species which I have described below. In other forms, however, from the Lower 

 and Upper Green Sand which agree with the typical species of Elasmostoma in 

 general form, and in possessing a smooth surface penetrated with large apertures on 

 one surface of the wall, the spicular structure of the fibres more nearly corresponds 

 to the Corynella type, and I have therefore separated these into a distinct genus. In 

 some, if not all, of these latter forms distinct canals are present, whereas, according 

 to Zittel, canals are absent in typical species of Elasmostoma. 



Elasmostoma acutimargo, Rcem. sp. 



1839. Tragos acutimargo, F. A. RcEin. Verst. d. Nordd. Oolit. Nachtr. p. 10, t. 17. f. 26. 

 1859. Elasmostoma frondescens, From. Introduction, p. 43, t. 3. f. 6, 6 a. 

 1864. Elasmustoma acutimargo, Eoem. Pal. Bd. 13, p. 45, t. 1. f. 21. 

 1878. Manonpeziza, Quenst. pars, Petref. Bd. 5, p. 362, t. 132. f. 39. 

 1878. Elasmostoma acutimargo, Zitt. Studien, III Ab. p. 44. 



Sponges growing in small fan-shaped expansions from 2-S to 37 ram. in height and 

 from 24 to 41 mm. in width. The walls are from 2 to 4 mm. in thickness. On the 

 upper or concave surface, though occasionally on the under surface, there is a smooth, 

 apparently compact, dermal layer perforated with circular or irregular apertures from 

 1-7 to 3 mm. in diameter. On the opposite surface are shown the reticulated fibres, 

 with small, irregular apertures between them. The fibres, as seen in a transverse 

 microscopic section, are from "17 to -31 mm. in thickness; the spicular structure is 

 but faintly shown, but it appears to be of the Sestrostomella type. 



Distribution. Neocomian, Censeau, Jura : Nogerais ; Berklingen, Brunswick. 



Elasmostoma Noemanianum, UOrhigny, sp. 



1847. Cupulospongia Normaniana, D'Orbiguy, Prodr. de Pal. vol. ii. p. 188. 

 1840-47. Spongia Peziza, Mich, (non Goldf.) Icon. Zooph. p. 143, t. 36. f. 5. 



1864. Elasmostoma Normanianum, F. A. Rcem. Pal. Bd. 13, p. 45, t. 16. f. 6. 



1871. Elasmostoma Normanianum, Gein. Pal. Bd. 20, p. 36, t. 7. f. 7-12. 



1878. Manon peziza macropora, Quenst. Petref. Bd. 5, p. 361, t. 132. f. 35. 



1878. Elasmostoma Normanianum, Zitt. Studien, III Ab. p. 44. 



1883. Elasmostoma Normanianum, Dun. Pal. Bd. 29, p. 41, t. 38. f. 4, 5. 



Sponges fan-shaped, or by the coalescence of the margins becoming obliquely cup- 

 shaped. The examples vary from 24 to 51 mm. in width, and from 22 to 42 mm. in 

 heieht : the walls are from 3 to 5-5 mm. in thickness. One surface of the Avail, either 

 the exterior or interior, is smooth, and perforated with circular apertures from 1 to 

 2 mm. in width, and about the same distance apart from each other ; the margins of 

 the apertures slightly project. The opposite surface only shows the irregular inter- 

 spaces between the fibres. According to Dunikowski, the fibres exhibit relatively 

 large axial three-rayed spicules, characteristic of the Sestrostomella type. 



