32 LOWER AND UPPER SILURIAN FORMATIONS: 



FIG. 6. 



forming altogether a wonderful example of the elaborateness 

 of pattern on which nature sometimes works ; and yet it is a 

 very humble animal, only, indeed, a stomach with arms 

 wherewith to supply itself with food. The echinodermata, 

 however, to which order it belongs, are the destructives of 

 their grade. The true crinoidea do not make a prominent 

 appearance in the Lower Silurians, and certainly not in such 



a style in England as to allow of 

 species being determined. But there 

 appears in these rocks what is con- 

 sidered by some as a lower crinoidal 

 form, in the Cystidea, a family in 

 which the tentacula are usually 

 wanting. In the words of the emi- 

 nent geologist, M. de Verneuil, this 

 family is the more interesting, since 

 " it seems to have preceded the other 

 crinoidea in order of time, and pre- 

 sents, as it were, the primitive form 

 of animals of this class." What is 



further remarkable, it makes little 

 Caryocnmtes ornatus, one i .-i T cri 



of the Cystidea. appearance above the Lower Silu- 



rians. 



By far the most conspicuous fossils of the Lower Silurian 

 formation, are JBrachiopods, part of the bivalve order to which 

 lingula belongs. This is a family of mollusks now slenderly 

 represented on earth ; in those early ages it was both abun- 

 dant and extensively diffused. The animal is a humble one 



A. 



FIG. 7. 



B. 



A, Terebratula reticularis; B, Interior of Spirifer hystericus. 



in- its class, having its two valves not connected by a hinge, as 

 is usual in superior bivalves, but kept together by a bundle of 



