SPHvEROSPONGIA. 137 



The hexagonal spicular plates, forming the outer surface of the Sponge, are 

 nearly flat, with a small central rounded elevation, which, however, is only seen in 

 the best-preserved specimens ; the plates also exhibit delicate concentric lines, 

 resembling lines of growth, and occasionally their margins are slightly elevated. 

 The plates near the base of the Sponge are the smallest, whilst those of the middle 

 and upper portions are about equal in size. They vary from 2*5 mm. to 7*5 mm. 

 in width. Though apparently the plates are in close contact with each other, 

 yet many specimens show narrow linear interspaces between their margins. 



The transverse spicular rays, forming vertical and concentric ridges within the 

 Sponge, gradually taper from their central node and terminate obtusely ; those 

 extending horizontally are not infrequently curved and less regular than those of 

 the vertical ridges. The rays are slightly unequal in length, and frequently 

 overlap, so that when fused together by fossilization their individual forms are not 

 readily distinguishable. 



As a general rule, the specimens showing the exterior surface are infilled with 

 a solid calcareous matrix, whilst in the hollow specimens the surface-plates are 

 concealed by the rock. Fragments, however, occur in which both the outer and 

 inner structures of the wall can be recognised. In all the specimens discovered, 

 the structures are replaced by carbonate of lime. 



In a lately published paper, 1 Prof. Schliiter proposes to include as distinct 

 species of Sphcerospongia, Scyphia cornucopia?, Goldfuss, Pasceolus Rathi, Kayser, 

 and Dictyophyton gerolsteinense, F. Roemer, as well as three new species, 

 8. sculpta, 8. vichtensis, and 8. megarhaphis. The characters of these species 

 for the most part depend upon slight differences in the size of the specimens and 

 of the individual spicular plates of their surfaces, and the specimens are very 

 fragmentary. Judging from the great variability in these features shown in the 

 suite of specimens of 8. tessellata from Newton- Bushell, I do not think these 

 differences have any specific value, at least as regards the forms described by 

 Goldfuss, Kayser, and F. Roemer, whilst I hesitate to express an opinion as to the 

 new species proposed. 



The type of the species, represented on PI. IV, fig. 2, is now in the Museum of 

 the Geological Survey, Jermyn Street. 



Distribution. — Middle Devonian : Newton-Bushell, Devonshire. Also at Vilmar, 

 Nassau ; Eifel, Germany ; River Jolva, near Bogoslofsk, Ural, Russia. 



1 ' Zeitschr. d. deutschen geolog. Gesellschaft,' 1887, p. 1. 



