54 SILICEOUS SPONGES. 



have to be amended, so as to include sponges in which the body-spicules have 

 expanded extremities, as well as those with attenuated and pointed ends to the body- 

 spicules. 



The figure given by Miss Benett, loc. cit. t. 8. f. 1, leaves no doubt as to the 

 identity of the form represented, for there is no other sponge from the Wiltshire 

 Chalk with the peculiar elongated compressed stem or root shown in her figure. 

 There is no certainty, however, that the figure of Chenendojwra oMiqua*, Michelin, 

 represents the same species as Polypothecia obliqua, Benett. 



This species appears to have been very common in the Upper Chalk. As a rule 

 the specimens are inclosed in the hollows of fiiuts, and exhibit, when thus preserved, 

 the spicular structure of the surface in a very beautiful manner. Generally the stem 

 of the sponge with only a small portion of the body is preserved, and in many 

 instances the stem alone remains in the interior of the flint. A few examples have 

 been preserved in the Chalk of Flamborough, and in these the body-wall remains and 

 the stem is usually wanting. In one example from this locality the sponge is nearly 

 flat and platter-shaped, and instead of a single central stem it gives ofi" from different 

 parts of its under surface numerous small rod-like processes. 



Distribution. Upper Chalk : Flamborough ; Beckhampton, near Brighton ; War- 

 minster, Stockton, Upware. 



Genus NEMATINION, Hinde, n. g. 



Sponges simple, elongate, rod-like in form, with a relatively small cup-shaped 

 summit, supported on a long cylindrical simple or bifurcated stem, which is either 

 branched or obtuse at its lower extremity. Below the cup vertical canals extend 

 throughout the length of the stem. The exterior surface is thickly covered with the 

 apertures of horizontal canals. The skeleton is composed of elongated, smooth, 

 thread-like spicules, which bifurcate near their extremities. These spicules are 

 interlocked together by their filiform extremities so as to form an open mesh- 

 work. • 



The peculiar feature of this genus is the small inconsiiicuous cup carried on the 

 summit of a very long stem. In its general form, and in the character of the 

 spicules, the genus approaches Carterella, Zitt. ; but this latter genus has a rounded 

 summit, and the spicules, as a rule, are knobbed and blunted at their ends. 



Nematinion caltculum, Hinde, n. sp. (Plate X. figs. l,la,lb,l c.) 

 The rod-like stem of the sponge is either straight or sinuous, usually simple, 

 though bifurcate examples occur. There is great variation in the length of different 

 specimens: the largest form which is in the collection is 310 mm. in length by 



* Icon. Zooph. p. 132, t. 41. f. 2 a, b. 



