190 
SILUKIA. 
[Chap. IX. 
species of Heliolites, together with the doubtful Stromatopora striatella, 
are still more abundant in the upper division of the system. 
Of Crinoids, or the lily-shaped tenants of the deep, most of which were 
attached by their root or base to submarine rocks, the inferior strata of 
the Silurian epoch have in general afforded fragments only. Referring the 
reader therefore to the Plates XIII.-XY. of this work, as containing the forms 
best known in the Silurian rocks when my work was published, it is enough 
now to state that, for the most part, broken portions of the stems only of En- 
crinites have been detected in the earlier portion of these deposits in Britain. 
One brilliant exception, however, is the Glyptocrinus basalis, M'Coy, a Orinoid 
found in the Lower Silurian slates of North Wales : 
fine specimens of it are to be seen in the Museum of 
Practical Geology in Jermyn Street, and in the 
Woodwardian Museum at Cambridge. One or two 
species have been met with in the Llandeilo Flags 
of Shelve, Shropshire. 
Next in order come those remarkable animals 
whose globular forms and strong external plates 
have enabled them to resist destruction better 
than the delicately constructed and slender-stemmed 
Encrinites : these are the Sphseromtes of old au- 
thors ; they are the Cystidea of Von Buch. 
Abounding in the Lower Silurian of Scandinavia 
and Russia, they were long ago described by Lin- Glyptocrinus basalis, M'Coy. 
nseus and Gyllenberg, whilst they have had much A Lower Silurian crinoid. 
new light thrown on their natural affinities by Von 
Buch, Volborth, the Due de Leuchtenberg, Edward Forbes, F. Roemer, J. Hall, 
J. Rofe, and others. They constituted, in the primeval era, the representatives of 
the Sea-urchins or Echinidae of the Secondary and Tertiary periods and of the pre- 
sent day. They have affinity with Crinoids on the one hand (some possessing very 
perfectly formed arms and tentacles) and with Sea-urchins on the other *, and 
have been divided into genera called Echinosphserites, Carj^ocystites, Sycocystites, 
Hemicosmites, Cryptocrinites, &c, some of which are here figured f. 
They usually occur in clusters, on the shaly surface of beds of limestone, re- 
sembling bunches of enormous grapes ; and in Sweden and Russia, where thus 
developed, they are associated with Orthidae and other Shells of the Lower Silu- 
rian rocks. In Britain they had not been found when the Silurian classification 
was first published ; but by the researches of the Government Surveyors they 
have been detected, and somewhat plentifully, in strata first described by me 
as Llandeilo Flags, at Sholeshook, Pembrokeshire, but now known to belong 
to the Caradoc rocks (p. 74). Indeed in Britain they are not observed to occur 
lower down in the series J, although in Bohemia some species are found in 
rocks of the age of the Lingula-flags. 
The usual forms in our country are species of Eclrinosphserites and Caryocys- 
* The views expressed in the text are those of crinen,' Bull. Sc. Acad. St. Pe'tersbourg, t. x., and 
Edward Forbes. The Cystidea, at least several Bull. Phys. Math., ib. t. iii. No. 6; Beschr. Thier. 
of them, have a close affinity with the Pentremites Silur. Kalk. v. Max. Herz. v. Leuchtenberg, St. 
of the Mountain-limestone. Petersb. 1843; and E. Forbes, Mem. Greol. Surv. 
t Other forms of these Cystidea are given in 1848, vol. ii. pi. 2. 
the work, ' Russia and the Ural Mountains,' vol. ii. J Remains of Cystidea are now said to occur in 
See also Von Buch, ' uber Cystideen,' Trans. Ber- the ' Primordial zone ' of St. David's, Pembroke- 
lin. Acad. 1845 ; Volborth, « iiber die Echino-En- shire. 
