202 
SILURIA. 
[Chap. IX. 
The Tentaculites and Cornulites of the earlier primeval strata must also be 
mentioned as remains of animals of this order, being probably Worms with 
shelly tubes like those of Serpula, but distinguished easily by their annulated 
form and cellular structure * (see PI. XVI. f. 3-10, for the form and magnified 
sections of C. serpularius). Tentaculites Anglicus, PI. I. f. 3, in Britain, is a 
characteristic Caradoc fossil ; but is also found abundantly in the Llandovery 
rock (T. scalaris of the Sil. Syst. is thought by some to be the interior cast of 
it). Cornulites serpularius is a cosmopolite of this age, ranging from Sweden 
to North America ; but, unlike the Tentaculite just mentioned, it ascends from 
the Lower Silurian strata, where it is rare, to the very summit of the Ludlow 
rocks. 
Crustaceans. — Nearly all the Articulata, besides the Annelides above 
mentioned, which have yet been detected in the Lower Silurian rocks 
belong to the extinct family of Entomostracous Crustaceans called Trilo- 
bites. The Silurian era was evidently one in which these animals flou- 
rished most ; for they became infinitely less abundant in the Devonian, 
and expired before the close of the Carboniferous era, during the earlier 
part of which, as will hereafter be seen, very few of their genera prevailed 
or lived on. As already indicated, we find some Trilobites in the oldest 
accumulations in which animal remains occur f ; and it is now to be re- 
marked that whilst, on the whole, certain genera and species of these 
creatures are more exact indicators of the successive strata than the other 
classes of animals, and that several genera are absolutely peculiar to the 
Lower Silurian rocks, there are some species, widely diffused over the 
world in strata of this era, which are common to both divisions. 
The researches of Messrs. Hicks and Salter in the lowest part of the ' Primor- 
dial ' Silurian rocks of St. David's Head, in South Wales, have resulted in 
adding many new species to the fauna of this series. In the annexed diagram 
(Foss. 45) will be found some of the chief forms of Trilobites that occur in the 
lowest Lingula-flags. The occurrence of three new species of Paradoxides (P. 
aurora, P. Davidis, and P. Hicksii, of Salter), added to the already well-known 
P. Forchhammeri, Angelin, tends to link on still more strongly the Silurian fauna 
of these islands to that of Sweden and Norway. 
Olenus micrurus, fig. 2, and 0. cataractes, fig. 3, together with Agnostus 
princeps, fig. 4, are all found in the black Lingula-schists of North Wales. The 
last, A. princeps, occurs in the Black Shales of the Malvern Hills, as well as in the 
Upper Lingula-flags of Penmorfa and the Tremadoc Slates of Portmadoc. Co- 
nocoryphe depressa, Salter (Ellipsocephalus ? of my former edition, p. 47, Foss. 7. 
fig. 2), is a Lower Trsmadoc Species, and may probably be found to occur in the 
Upper Lingula-flags when these shall have been more carefully examined. C. 
invita, Salter, from the Upper Lingula-flags of Penmorfa (Tremadoc), so closely 
resembles C. Emmerichii of Barrande that it may almost be mistaken for that 
* These fossils, Tentaculites and Cornulites, t For example, in the Cambrian rocks of the 
have been assigned to various groups of animals, Longmynd, in the Alum-slates of Sweden (Be- 
the notion that they were parts of crinoidal crea- giones A. B. of Angelin), in the Lingula-slates of 
tures being the most generally accepted. They North Wales, and in the Lowest Silurian of the 
were, however, shelly tubes, of a highly complex United States. This is the zone to which M. 
cellular structure, not jointed tentacles or stems, Barrande first attached importance ('Zone primor- 
and could by no means be parts of such animals, diale ') by working out its very peculiar and re- 
— J. W. S. markable fauna in Bohemia. 
