176 CALCAEEOUS SPONGES. 



tures, as in the preceding species. The outer surface is even, or with slight swellings 

 and constrictions. 



The walls vary from •24 to -4 mm. in thickness ; the perforations and the spicular 

 structure of the fibres are the same as in T. anastomans. 



This species differs from T. anastomans in the larger size of the individual sponges, 

 the more delicate walls, and the irregular character of the interior cliambers. Its 

 mode of growth differs from that of T. annulatus. Keeping, sp. ; but as the interior 

 characters of this species are not stated, it is not possible to make a comparison of 

 these features in the two species. 



Distribution. Lower Green Sand : Farringdon and Upware. 



Tremactstia clavata, Keeping, sp. (Plate XXXIV. fig. 6.) 



1883. VerticeUites clavatus, Keeping, Fossils of Upware &c. p. 146. 



1869. Discoplia helvetica, Loriol, pars, Mon. Foss. de Landeron, p. 65, t. 5. f. 8. 



Sponges growing singly or in small colonies. The individual sponges are obconical 

 in form, from 25 to 52 mm. in height, and about 14 mm. in diameter. The partitions 

 between the chambers are nearly horizontal, and about 2"75 mm. apart. The central 

 cloacal tube is continuous, elliptical in section, and about 4 mm. in diameter. It is 

 perforated by a circular series of relatively large apertures, with collar-like projec- 

 tions, which open into each chamber. 



The walls are from "25 to '5 mm. in thickness ; the perforations in them are similar 

 to those of the two preceding species. The form and size of the sponge distinguishes 

 this from all other species of the genus. It is compai-atively rare. 



Distribution. Lower Green Sand : Farringdon and Upware. 



Genus ELASMOCCELIA, Ecemer, 1864. 



Elasmoccelia crassa. From. sp. (Plate XXXIIl. fig. 11.) 



1861. Elasmojerea crassa, From. Cat. raisonne, p. 10, t. 2. f. 10. 

 1878. Elasmoccelia crassa, Zitt. Studien, III Ab. p. 34. 



The anastomosing walls of the sponge are from 5 to 6'5 mm. in thickness ; a single 

 row of cloacal tubes, about 1"75 mm. in width and the same distance apart, extends 

 the length of the crest of the walls. The fibres of the outer surface are so closely 

 arranged that there are only minute circular pores, about T6 mm. in width, between 

 them. The fibrous mesh of the interior of the wall is relatively open ; the fibres are 

 about "2 mm. in thickness. 



There is but a single example of this species in the Museum ; the walls are some- 

 what thinner than in Fromentel's type, but the differences do not appear to me to 

 be sufiicient to constitute a distinct species. 



Distribution. Lower Green Sand: Farringdon, Berkshire. 



