88 SILICEOUS SPONGES. 



sponges, I am unable to determine whether the resemblance is more than in outer 

 form. 



Distrihution. Upper Chalk : Wiltshire. 



Phymaplectia spinosa, Hinde, n. sp. (Plate XXI. figs. 2, 2 a.) 



Sponges with convolute walls, from 5 to 7 mm. in thickness, which coalesce at 

 their margins and become funnel-shaped. The margins are rounded ; the basal 

 portion has not been preserved. The exterior surface is fm-nished in places with 

 small, straight spinous processes. A specimen is 92 mm. in height, and the same in 

 width at the summit. 



Traces of sinuous canals, -5 mm. in width, are apparent in one part of a specimen, 

 but I cannot determine if these are generally present. The interior spicular mesh is 

 of the same character as in the preceding species, but the spicules are somewhat 

 more robust. The outer surface retains in places the smooth dermal layer ; the 

 spicular heads of which it is formed are about -25 mm. in extension. The inner 

 surface of the cup is not exposed. 



This species approaches very closely to P. irregularis, but the spicules of its interior 

 mesh are somewhat larger, and those of the dermal layer smaller, than in the last- 

 named species. The specimen figured belongs to the Jermyn-Street Museum. 



Distribution. Upper Chalk: Wiltshire (Cunnington coll.). 



Phymaplectia cribeata, Iliiule, n. sp. (Plate XXI. figs. 3, 3 a.) 



Wall-plate of sponge growing in wavy folds, showing also slight concentric, 

 rounded ridges on the outer surface. The wall is from 4 to 5 mm. in thickness. 

 The basal portion of the specimen is not preserved. The imperfect example is 

 82 mm. in height and 112 mm. in width. 



The spicules of the interior mesh are very closely tuberculated ; the arms are 

 about "4 mm. in length, and more robust than in the preceding species. The outer 

 surface of the sponge-wall is covered with a smooth dermal layer, which is penetrated 

 with numerous minute pores about "1 mm. in diameter, and only visible under a good 

 lens. The dermal layer between these pores is in part composed of extremely minute 

 trifid spicules, the head-rays of which are about -1 mm. in extension, in part of 

 apparently irregular spicular bodies, whose forms are not sufficiently well-preserved 

 for determination. 



The mode of growth, and more particularly the characters of the dermal layer, 

 readily distinguish this species from the preceding. The only specimen known is 

 from the interior of a flint. It belongs to the Jermyn-Street Museum. 



Distrihution. Upper Chalk: Wiltshire [Ciinnington coll.). 



