472 
ELEMENTS OF GEOLOGY, 
Fig. 552. 
Fig. 553. 
youug individuals of Trinucleus 
concentricus {T, ornatus, Barr.). 
a. Youngest state. Natural size 
and magnified; the body rings 
not at all developed, b. A little 
older. One thorax joint, c. Still 
more advanced. Three thorax 
joints. The fourth, fifth, and 
sixth segments are successively 
produced, probably each time 
the animal moulted its crust. 
Shropshire; N. America; Bohemia. 
Shropshire, are in fact identical in age, and contain the same 
organic remains. At Bala, in Merionethshire, a limestone rich 
Fig. 554 . in fossils occurs, in which 
two genera of star-fish, I^ro- 
taster and Palceaster^ are 
Palceaster asperimus, Salt. 
pool. 
found ; the fossil specimen 
of the latter (Fig. 554) being 
almost as uncompressed as 
if found just washed up on 
the sea-beach. Besides the 
star-fish there occur abun- 
Caradoc, Welsh- dance of those peculiar bod- 
• ies called Cystidece, They 
are the Sphmronites of old authors, and were considered by 
Professor E. Forbes as intermediate Fig. 555 . 
between the crinoids and echino- « 
derms. The Eehinosphceronite here 
represented (Fig. 555) is character¬ 
istic of the Caradoc beds in Wales, 
and of their equivalents in Sweden 
and Russia. 
With it have been found several 
other genera of the same family, such 
as Sphceronites^ Hemieosmites^ etc. 
Among the mollusca are Pteropods ^ 
of the genus Gonularia of large size EcMnosphceronitesbaiUctis^’EAetL- 
(for genus, see Fig. 518, p. 453). 
About eleven species of Graptolite 
are reckoned as belonging to this 
formation; they are chiefly found in peculiar localities where 
wald. (Of the family Cystidece.) 
Mouth, h. Point of attach¬ 
ment of stem. Lower Siluri¬ 
an S. and N. Wales. 
