VENTRICULITES—FOSSIL SPONGE (CHALK).
From the earliest ages the corals play a conspicuous part in fossil history; and as in our days we find them encircling islands and fringing continents with huge ramparts of limestone, so many an ancient reef, now far inland, and raised several thousand feet above the level of the sea, bears witness to the vast terrestrial changes that have taken place since it was first piled up by the growth of countless zoophytes.
SIPHONIA COSTATA—FOSSIL SPONGE (GREEN SAND, WARMINSTER).
With regard to the dimensions of the fossil corals we do not find that any of them exceeded in size their modern relatives; but their construction was widely different.
The fossil sponges of the primitive seas are likewise very unlike those of the present day.
Thus in all the ancient strata we find abundant spongidæ with a stony skeleton, while all the modern sponges possess a horny frame. The Petrospongidæ, or stone sponges, which have long since disappeared, are frequently shapeless masses; but a large number are cup-shaped, with a central tubular cavity, lined, as well as the outer surface, with pores more or less regularly arranged.
ENCRINUS LILIIFORMIS.
(Muschelkalk, Germany.)
