564 CARADOC AND BALA BEDS. [Ch. XXYH. 



his figures of the metamorphoses of the common Trinucleus are 

 copied in the foregoing woodcuts (figs. 646, 647). 



In Mr. Salter's monograph of the British trilobites, he expresses 

 his opinion that their habit was to live on the sea-bottom and devour 

 the silt charged with organic matter as sea-worms do, or else, possi- 

 bly, to devour the worms themselves. He supposes the trilobite to 

 have had no jaws, and to have been provided with a suctorial 

 mouth.* 



It has been ascertained that a great thickness of slaty and crys- 

 talline rocks of South Wales, as well as those of Snowdon and Bala 

 in North Wales, which were first supposed to be of older date than 

 the Silurian sandstones and mudstones of Shropshire, are in fact 

 identical in age with the Caradoc formation now under considera- 

 tion, and contain the same organic remains. At Bala in Merioneth- 

 shire, a limestone rich in fossils occurs, and below it sandstones 

 some thousands of feet in thickness. In this limestone several rare 

 starfishes are found, and abundance of those peculiar bodies called 

 Cystidce. These last are amongst the most recent additions made by 

 palaeontologists to the Radiata. Their structure and relations were 

 first elucidated in an essay published by Yon Buch at Berlin in 

 1845. They are the Sphoeronites of old authors, and are usually 

 met with as spheroidal bodies covered with polygonal plates, with a 

 mouth on the upper side, and a point of attachment for a stem 



(which is almost always broken off) 

 on the lower (fig. 648 b). They 

 were considered by Prof. E. Forbes 

 as intermediate between the crinoids 

 and echinoderms. The Echinosphce- 

 ronite here represented (fig. 648) is 

 characteristic of the Caradoc beds in 

 Wales,f and of their equivalents in 

 Sweden and Russia. 



With it have been found several 

 other genera of the same family, such 

 BI . . ' _ „. „.,",- as Splicer onites, Hemicosmites. &c. 



Eclanosphcerttes balticus, Eichwald, sp. ± 7 



(Of the family Cystideoa.) Among the mollusca are Pteropods 



a. Mouth. f th e genus Conularia of large size 



b. Point of attachment of stem. ,„ „ n _. ■ ~ * n \ 

 Lower Silurian, S. and N. Wales. (for geilUS, see fig. 611, p. 540); 



Graptolites are rare, except in pecu- 

 liar localities where black mud abounds. The formation, when traced 

 into South Wales and Ireland, assumes a greatly altered mineral 

 aspect, but still retains its characteristic fossils. In Tyrol it is espe- 

 cially rich in organic remains.^ It is worthy of remark that, when it 



* Palseontographica, vol. xvi. p. 9, 1864. 



f Quart. Geol. Journ., vol. vii. p. 11 ; and Mem. Geol. Surv., vol. ii. p. 518. 



\ See Portlock's Report of Londonderry, 1843. 



