— 68 — 



leton is so close that it seems highly probable that they be- 

 long to Cystispongia. There is also a remarkable resemblance 

 between these fragments of mesh and the skeleton of Astj- 

 lospongia pracmorsa. Goldfuss and under the microscope there 

 was little difference to be noticed in the dimensions , form, 

 and arrangement of the spicular mesh of this Silurian sponge, 

 and the examples from the Upper Chalk. 



Coscinopora sp. 



(Plate V, figs. 22 — 24). 



Portions of skeletal mesh having circular or elliptical in- 

 terspaces of unequal dimensions; composed of the usual six- 

 rayed spicules with open or ' lantern > nodes at their centres. 

 Diameter of some of the larger interspaces 0,45 mm. Frag- 

 ments of outer or surface layer consisting of a delicate mem- 

 brane perforated with circular openings of different sizes, the 

 larger, which appear to be di.sposed at regular distances from 

 each other, have a diameter of 0,38 mm. Fragments of the 

 root-fibre composed of nearly straight spicular fibres with 

 transverse connections. 



These different portions of the structure of a Hexactinel- 

 lid sponge appear to correspond with the Genus Coscinopora 

 Goldfuss. The type of the genus C. infundibulijoi-jiiis, Goldf. 

 (Petref. Germ, i" Theil, p. 30, Taf. 30, fig, 10) is a cup 

 shaped sponge with thin walls, Mhich are co\ered by a deli- 

 cate perforate surface membrane similar to that of fig. 23. 

 The inner skeleton has .spicules with ' lantern nodes, form- 

 ing elliptical interspaces, which however are less regular 

 in their arrangement than in the Horstcad examples (fig. 22). 

 The sponge appears to have been attached to the sea bottom 

 by a root-like extension of the base, which is formed of 

 nearly parallel fibres of silica with transverse connections at 

 frequent intervals similar to that shown in fig. 24. Coscino- 

 pora iiifiuidihuliforniis appears to be abundant in the Upper 



