PEXGELLY — ON THE DEVONIAN AGE OF THE WORLD. 



341 



being confined to the Silurian rocks ; but is, perhaps, a complex 

 sponge.''* The fossil is, accordingly, catalogued at present under 

 the name of Splicer ospongia tesselatus. It occurs in the limestone 

 beds at Lummaton, near Torquay, and at Woolborough Quarry, near 

 Newton ; one fine specimen recently found at the latter locality, shows 

 that it is cup-shaped, the calyx, which unfortunately is somewhat 

 broken, is elliptical, — having, at the top, its greatest diameter, about 

 two and three-fourths inches, the least two inches, and narrowing 

 almost to a point at the bottom. The depth of the cup is about one 

 and a quarter inch. The walls are about one-twentieth of an inch 

 thick ; the inner surface is divided into a net- work of quadrilateral 

 meshes, by the interlacing of, what may be termed, vertical and 

 horizontal ribs. The former are, with slight variations, about three- 

 twentieths of an inch apart, and are of two kinds, — primary, extending 

 from the bottom to the top of the cup ; and secondary, springing 

 from various heights in the side or wall. The primary cycle consists 

 of sixteen; the secondaries occur in pairs one on each side of a 

 primary, of which they seem to be two branches issuing from the 

 same node ; these, in like manner, occasionally give off similar 

 branches. The horizontal ribs are less prominent, somewhat thinner 

 and closer than the verticals ; they are about one tenth of an inch asunder. 

 Not unfrequently some irregularity is observable in their arrange- 

 ment, being occasionally more or less out of horizontal, and not 

 always at quite the same level on the opposite sides of the same 

 vertical ; so that as often as otherwise, they are not hi one and the 

 same straight line. In fact they sometimes remind one of the 

 "bridging-pieces 1 ' which builders insert transversely between the 

 flooring joists in houses for the purpose of securing stability. The 

 surfaces of both sets of ribs, as well as the interstices, are covered 

 with granules. Imagine the cup to be a gigantic calyx of some 

 species of coral belonging to the sub-order Zoantharia tabulata, as, 

 for example, Heliolites porosa ; then do the vertical ribs represent the 

 rudimentary septa, and the horizontal ones the tabula?, which must 

 be considered as rudimentary also .J 



The beautiful specimen of this fossil figured in the Transactions of 

 the Geol. Soc, vol. hi., part 1st, plate xx., fig. 1 ; and also in Professor 

 Phillips' " Palaeozoic Fossils," plate lix., is lodged in the Jermyn 

 Street Museum. 



The genus Stromatopora, formerly regarded as belonging to the 

 corals, but now removed to the sponges, contain five Devonian 

 species, all of which appear to be confined to British localities, with 

 the exception of S. concentriea, which occurs also in the Eifel. It is 

 extremely abundant in the South Devon limestones, and not unfre- 

 quently attains a very great size. 



* Palaeozoic Fossils, p. 135. 

 f Siluria, 3rd Ed., p. 298. 

 J This is merely meant as illustrative, and not as a .suggestion that the 

 fossil is a coral. 



