34 SILICEOUS SPONGES. 



There are typical examples of this species in the Museum from the Craie of 

 Vaches Noires, near Havre, but only a single specimen from the Upper Green Sand 

 of Warminster, which I refer with some doubt to this species ; for there are no 

 traces of the wi-inkled dermal layer, and the marghis of the cup are rounded, and 

 not flattened as in the French examples. The spicular structure, however, appears 

 to resemble that of the typical forms ; and I therefore leave it provisionally under 

 this species. According to Prof. Zittel the French examples are derived from the 

 Upper Chalk, or Senon of D'Orbigny ; but I have not met with any from the same 

 horizon in England. 



Distrihution. Upper Green Sand : Warminster. Upper Chalk (Senon) : Vaches 

 Noires, near Havre. 



Chenendopora michelinii, Hincle, sp. n. (Plate III. figs. 1, 1 «, 1 b.) 



Sponges simple, with vasiform or cup-shaped bodies which gradually taper below 

 to an elongated cylindrical or compressed stem, which occasionally bifurcates in its 

 lower portion. The walls of the cup or vase are sometimes smooth and even, some- 

 times with longitudinal open folds ; the margins are usually thin, rounded, and 

 occasionally with a slight inward or outward curve. There is a considerable 

 variation in the thickness of the cup-walls in diff'erent specimens ; the vasiform 

 examples range from 5 to 6 mm. in thickness, whilst the cup-shaped forms are even 

 9 mm. thick. The stem is usually simple, but at its lower portion it either divides 

 into root-like extensions or becomes expanded into a hollow disk. In large speci- 

 mens the stem measures 260 mm. in length by 46 mm. in thickness; and the width 

 of the sponge at the summit varies in different examples between 55 mm. and 

 170 mm. 



Both the exterior and interior surfaces of the cup are furnished with numerous 

 openings of canals about 0'85 mm. in width, and apparently similar on both surfaces. 

 The stems when weathered exhibit longitudinal branched canals. 



The spicules are irregular branching bodies, covered with rounded tubercles, which 

 interlock and connect them with each other. They are so intimately interwoven 

 together that in a thin microscopic section it is difiicult to distinguish the individual 

 forms. Occasionally a sinuous canal can be seen in the axial line of the spicule. 

 The spicules are 0"042 mm. in thickness. 



The sponges which I refer to this species are not uncommon in the Upper Green 

 Sand of Wiltshire. There is a considerable variety of form and dimensions in the 

 difiierent examples ; but 1 cannot discover any characters which would allow them to 

 be placed under more than a single species. They seem to have been generally 

 referred to the Polypothecia vifundibuhim, Benett ; but in the figure of this species 

 three or four cup-shaped sponges are represented as growing closely aggregated 

 together, whilst C. michelinii is uniformly simple. In the absence of any description 



