CCELOSCTPHIA . — POLTBLASTIDirM. 119 



wall-plaits are '5 mm. in thickness. The spicular mesh is small ; the octahedral 

 nodes are '3 mm. apart. The characters of the dermal layer are obliterated, and the 

 interior spicular structure is only preserved in one or two places. The type speci- 

 men, the only one at present known, is in the Jermyn-Street Museum. 



Distribution. Spongarian zone of tlie Chloritic Chalk {Tate) = Upper Chalk : 

 Island Magee, near Belfast. 



Genus POLYBLASTIDIUM, Zittel, 1877. 



POLYBLASTIDIUM LUXUEIANS, Zltt. 



1877. Polyblastidium luxurians, Zitt. Studierij I Ab. p. 52; Neucs Jahrbuch, p. 363, 

 t. 3. f . 7. 



Microscopic portions of the spicular structure of this species. 

 Distrihution. Upper Chalk : Linden, Hanover {coll. Zitt.). 



POLYBLASTIDIUM EACEMOSUM, Toulm. Smith, sp. (Plate XXVII. figs. 2, 2 a.) 

 1848. Brachiolites racemosus, T. Smith, Ann. Ss Mag. Nat. Hist. vol. i. p. 364, 1. 15. f. 6. 



Body of sponge club- or pear-shaped, supported on a slender stem, with divergent 

 rootlets at its termination. From the surface of the sponge short projecting hollow 

 tubes, from 8-5 to 14 mm. in diameter, project irregularly outwards. An average 

 specimen is 77 mm. in length by 40 in width. 



The examples of this species are all in solid flint, and only transverse sections of 

 the tubular projections are shown on the outer surface of the flint. The walls of 

 the tubes are 2-5 mm. in thickness ; they are formed of regular plaits, '5 mm. thick. 

 The spicular mesh appears to be irregular; the distance between the octahedral 

 nodes is •25 mm. 



This species differs from P. luxurians, Zitt., by the larger size and lesser number 

 of the projecting tubes. 



Toulmiu Smith's figure is diagrammatic, and a very inaccurate representation of 

 the original. 



Distribution. Upper Chalk : Kent, Sussex {coll. T. Smith). 



Polyblastidium tuberosum, Toulm. Smith, sp, 

 1848. Brachiolites tuberoms, T. Smith, Ann. & Mag. Nat. Hist. vol. i. p. 354, 1. 15. f. 3. 

 The type of this species is a fragment of a sponge, which has been partially cleaned 

 from a chalky matrix. Only the general form, indicated by markings in iron per- 

 oxide, can be distinguished. The body of the sponge appears to have been a thin- 

 walled, hollow, subcylindrical tube, with small bud-like projections on its exterior 

 surface. The tubular axis is about 46 mm. in length by 16 in width. The pro- 

 jecting buds are 8 mm. in length ; their summits are expanded and slightly concave. 



