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which also form irregular furrows on the surface of the skeleton, 

 beneath the dermal layer. By the careful removal of the 

 matrix, the dermal laminae can be seen in places on the 

 surface of the sponge which they appear to have completely 

 covered and the differently-shaped laminae arc present in the 

 same individual sponge. A comparison with the type spe- 

 cimens show such a close agreement both of the mesh and 

 dermal spicules that there can hardly be a doubt, but that 

 these Horstead spicules belong to the same species. P. squa- 

 mosa is from the Upper Chalk of Ahlten in Hanover. 



Genus Ragadinia, Zittel 1878. 

 Ragadinia annulata n. sp. 



(Plate IV, figs. 24—30. Plate V. figs. 1—4.) 



Spicules of the mesh (PI. V, figs, i — 4) minute, irregularly 

 four-armed ; frequently one arm truncated and having a round 

 knob at its termination; the other arms having a single 

 prominent ring-shaped expansion a short distance from the 

 centre, but otherwise with smooth surfaces. These arms bi- 

 furcate and terminate in irregular twig-like extensions, which 

 interlock with each other to form the mesh. Length of spicular 

 arms varying from 0,27mm. to 0,74mm.; and in thickness 

 between 0,067 mm., and 0,135 mm. Surface spicules (PI. IV, 

 figs. 24 — 30) composed of spicular discs, more or less lobed 

 and branched, and having a rudimentary shaft. These discs 

 vary in diameter between 0,675mm. and 1,26mm. 



The mesh spicules of this species are very distinctly 

 marked off from any other of the allied forms by the peculiar 

 ring-shaped swelling with which the arms are furnished. One 

 arm of the spicule extends but a short distance from the 

 central point and then expands into a prominent rounded knob ; 

 the other three arms radiate irregularly from the centre, near 

 which each has the ring-shaped swelling, and then rapidly 



