120 SILICEOUS SPONGES. 



No aperture can be detected in the summit of the buds ; but the condition of the 

 specimen is too imperfect for satisfactory determination. The figure of T. Smith's 

 is to some extent a restoration of the original specimen. The closed summits of the 

 bud-like projections distinguish this species from P. luocurians, Zitt. 

 Distribution. Upper Chalk: Kent] {coll. T. Smith). 



Genus CEPHALITES, Toulm. Smith, pars, 1848. 

 Toulmin Smith included in this species a variety of forms, which have been sepa- 

 rated by Prof. Zittel into two or three genera. As restricted by Zittel, the genus 

 only includes those sponges which resemble Ventriculites in the foldings of the plaits 

 of the wall, and possess the further characteristic that the summit of the sponge- 

 wall is truncate and covered with a delicate siliceous membrane. 



Ckphalites longitudinalis, Toulm. Smith. 



1847-48. Cephalites longitudinalis, T. Smith, Ann. & Mag. Nat. Hist. 1st ser. vol. xx. t. 7. 



f. 1, and 2nd scr. vol. i. t. 14. f. 1. 

 1848. Cephalites guttatus, T. Smith, ib. 2nd ser. vol. i. t. 14. f. 2. 

 1878. Cephalites longitudinalis and guttatus, Zitt. Studien, I Ab. p. 52 ; Neues Jahrbuch, 



p. 3G3. 



Sponges narrow, funnel-shaped, with a short slender cylindrical stem, terminating 

 in divergent rootlets. An average specimen is 68 mm. in length, and 25 in width at 

 the summit. The wall varies from 4 to 13 mm. in thickness in different individuals. 

 The exterior surface is formed by a series of longitudinal ridges about 3 mm. in width, 

 more or less sinuous, and occasionally interrupted transversely so as to form rows of 

 projecting bosses. The inner surface has numerous circular canal-apertures, 1'5 mm. 

 wide, disposed in quincunx. The plaits forming the wall are about 1 mm. in thick- 

 ness. The spicular mesh is irregular ; the distance between the spicular nodes is 

 about "25 mm. 



I am unable to detect specific differences between C, guttatus and C. longitudinalis. 

 Even in the same specimen the outer surface will occasionally exhibit continuous 

 ridges and rows of projecting bosses. The examples of this species are common; 

 they are nearly all preserved in chalk, and the spicular structure is usually in the 

 condition of iron peroxide. In some examples of this and other species of the genus 

 this replacing material is sufficiently firm for the .spicular mesh to remain intact after 

 careful removal of the matrix, but it is of an extremely delicate character. 



Distribution. Upper Chalk : Glynde, Westmeston, Sussex ; Shalford, Surrey ; 

 Maidstone, Dover, Kent (coll. T. Smith). 



