GEOGNOSY AND GEOLOGY. 149 
Stromatopora concentrica (fig. 1) exhibits a corolla with fine furrows 
distributed concentrically on a spherical surface. Tragos acetabulum 
(fig. 2), similar to the last, cup-shaped, with irregular pits. Syringopara 
bifurcata (fig. 3), Catenipora escaroides (fig. 4), C. labyrinthica (pl. 42, 
jig. 65). The Syringopora are distinguished from the Catenipora by the 
position of the tubes in which the polyps lived. In both, these are straight ; 
but while those of the former ramify, and have internal walls, those of the 
latter are arranged singly one after the other; their extremities forming 
chain or net-like figures. Aulopora is a somewhat similar genus, of which 
A. serpens (pl. 37, fig. 7) is of most frequent occurrence. The small 
tubular cavities are combined in a reticulation, by which they are 
distinguished from the preceding. Cyathophylle and Astree are also 
somewhat similar: while, however, the former grow up separately, and may 
even ramify, in the latter the individual portions are fused together. P/. 
37, jig. 5, represents Cyathophyllum cespitosum; pl. 42, fig. 64, C. 
hexagonum; pl. 37, fig. 6, Astrea ananas ; and pl. 42, fig. 66, A. porosa. 
These corals generally occur in associations forming large blocks ; others, 
again, as the Retepore, Gorgonias, and Favosites, are different in this 
respect. These are free, and consist of imbricated tubes, communicating by 
pores. Here belong: Favosites polymorpha (pl. 37, fig. 8), Retepora 
infundibulum (fig 9),and Gorgonia assimilis (fig.10). ‘The first star fishes 
were not free, like those of the present day, but were supported centrally on 
a jointed stem. A most interesting relation exists between the structure of 
the fossil Echinoderms and the embryological character of those of the 
present day. The succession of extinct and fossil forms is beautifully 
typified in the changes which the existing species of allied families pass 
through in their progress from the ovum to the adult. The oldest 
Echinoderms known in Paleontology, are the Cystidez, these being at 
the same time the most imperfect. They appear as spherical, armless bodies 
covered with plates, with an oral aperture on the upper part, an anal on the 
side, and fixed to the ground by a jointed stem. Then come the Crinoids, 
fixed like the last, but provided with jointed arms, whose motions sufficed 
to introduce food into the central mouth. Next appear the Ophiuras. 
animals with arms like the Crinoids, and fixed when young to a stem or 
pedicle, from which they become free when adult. Finally, we have the 
Asteroids, which immediately after birth possess arms and a free motion. 
The Cystidee occur in the transition rocks, but very rarely. Crinoids are 
more abundant. Of these, the individual fossils, as well as larger portions 
of the arms and stems, are frequently found and known as encrinital joints 
or bones. The crowns, however, are more rarely met with, and the cause 
of the separation of the parts is probably to be ascribed to the rapid 
decomposition of the integuments and consequent dispersion of the portions, 
produced by death. PJ. 37 represents Hypanthocrinus decorus, fig. 11, 
Cyathocrinus pyriformis, fig. 12, Dimerocrinus isodactylus, fig. 13. and 
Cupressocrinus crassus, fig. 14. 
Mollusca are of frequent occurrence in the transition slate. Of course 
the shells alone are found, the soft parts too readily undergoing decomposition. 
579 
