DESCRIPTIVE REMARKS. ‘i XX1x 
The diagram, fig. 7—an ideal representation or typical example of 
the order—is intended to show the various parts entering into its com- 
position and their designation. Like the corals, the ‘‘ Stone Lilies” at- 
tained their maximum in Upper Paleozoic strata, their remains being 
especially abundant in the Wenlock and Carboniferous Limestone. 
In the older Silurian strata they are comparatively rare, except as 
fragments; we have figured amongst the Llandeilo fossils (PI. vi., 
fig. 5) a portion of them referred to Cyathocrinus, which is said tv be the 
oldest crinoid known in British strata. A nearly complete example, 
named Glyptocrinus basalis is shown on Pl. x., fig. 7, as a Caradoc 
fossil, although they are seldom met with in so perfect a state in beds 
so low in the series. 
Tue Cystipera.—Spheronites of old authors, are plentiful in British 
strata, first appearing in Caradoc shales and limestone ; they abound in 
the Lower Silurian strata of Scandinavia and Russia. This group of 
the Echinodermata, allied to the crinoids by a resemblance of some parts 
of their structure, are mostly rounded bodies formed of a number of 
closely united polygonal plates, the stem or column being short or rudi- 
mentary. In some the arms and tentacles are only obscurely in- 
dicated (as in Pl. xvii., fig. 6) or entirely absent. The ‘“ pectinated 
rhombs”’ and ‘‘ pyramids,” or ovarian openings, such as are figured 
on the same Plate, figs. 6, 6 and c, are characteristic peculiarities of 
this group. The principal genera found in this formation are shown 
on Pl. x.—Spheronites, fig. 4 ; Echinospherites, fig. 5; aud Hemicos- 
mites, fig. 6. ; they include sixteen species, and probably represent in 
these older deposits the sea urchins or Echinide of modern seas. 
SrarFIsHEs not very unlike those of the present day occur for the 
first time, although not frequent, in Caradoc strata. Pleaster obtusus 
resembles so much the living Uraster as to have been originally re- 
ferred to that genus ; another smaller species, doubtfully named Pro- 
taster, and figured on the same Plate (9, a 6), appears to be allied to 
Ophuira, the brittle star. Sixteen species of starfishes are recorded 
from British strata—six in Lower, ten in Upper Silurian. 
The net-like Poryzoa, now considered as belonging to the lowest 
group of the Mollusca, but formerly classed with corals to which they 
certainly bear a close relationship, are more abundant in Upper Silurian 
strata. 
Fenestelia assimilis, pl. xi., fig. 1, which is also a common Wenlock 
species, 1s a good example of this class of fossils, and is not unlike some 
modern forms at present existing in the seas of Europe; it occurs abun- 
dantly in the Caradoc limestone of the Chair of Kildare. 
For comparison with this fossil and that of Dyctyonema, figured on 
Pl. i., fig. 2, which appears to be more closely connected with the 
Reteporide than to Graptolites, I have introduced a figure (woodcut 
fig. 8) of a small but well-marked recent species with enlarged portions, 
showing the arrangement and form of cells in this British species of net- 
work coral: from Johnston’s British Zoophytes, 2nd ed., woodcut 67, 
p- 854; and enlarged view of cells from Busk’s Polyzoa; Pal. Soc., 
PL xin, fig, 2. 
