52 SILICEOUS SPONGES. 



Pachypoterion robustum, Hinde, n. sp. (Plate IX. figs. 2, 2 <2, 2 h.) 



Sponges cup- or goblet-shaped, the walls very thick, so that in some examples the 

 cup is nearly filled with the siliceous skeleton. The body either gradually tapers to 

 the simple elongated, cylindrical stem, or there is a sharp constriction between the 

 base of the cup and the top of the stem. The specimens vary considerably in size : 

 small examples measure 110 mm. in length by 65 mm. in width, whilst larger forms 

 are 270 mm. long by 130 mm. in width. 



The canal-apertures in the interior of the cup are, in some examples, arranged in 

 concentric circles; they are about 2 mm. in width, and either elliptical or circular in 

 section. The apertures of the exterior surface vary between '5 and '9 mm. in width. 

 They appear to be disposed in a regular vertical series. In a horizontal section of 

 the base of the cup, the lateral canals appear as so many radiating lines extending 

 from the outer surface to near the central portion. The arms of the spicules measure 

 •135 mm. in thickness. 



This species appears to be abundant. The examples vary considerably in size, 

 thickness of the wall of the cup, and in the character of the stem ; but as there are 

 numerous gradations between the extreme forms, I have included them under a 

 single species, which may be distinguished from the next by the thickness of the 

 walls and of the spicules and the dimensions of the canals. 



Distribution. Upper Green Sand : Warminster, Pewsey, Sambourne, Folkestone. 



Pachypoterion compactum, Hinde, n. sp. (Plate IX. figs. 3, 3 a.) 

 1816. Alcyonite (funnel-form), W. Smith, Strata identified by Organic Fossils, t. 5. f. 12. 



Sponges cup-, vase-, or open funnel-shaped, with simple cylindrical stems. The 

 margins rounded. The walls of the body are from 5 to 9 mm. in thickness. The 

 width of the cup varies in different examples from 65 to 110 mm. 



The canals opening into the interior of the cup are 1 mm. in width, inconspicuous, 

 and irregularly distributed. Those extending from the outer surfiice to the interior 

 are very numerous, about "3 mm. in width, and nearly horizontal in direction. 



The spicules are of the same character as those of P. robustum, but of less thick- 

 ness ; they measure '09 mm. in width, and about '225 mm. in length. They are 

 very closely interwoven together, so as to form a compact network. 



This species is distinguished from P. robustum by its thinner walls, smaller 

 spicules, and more compact spicular tissue. 



The specimen figured is the original of William Smith's Alcyonite, loc. cit. t. 5. 

 f 12 ; but the lower portion of the stem is not represented. The interior of this 

 specimen is filled with the hard matrix. The spicular structure (fig. 3 a) is from the 

 exterior surface of the same example. 



Bistnbution. Upper Green Sand : Warminster ; Saumur. 



