SILURIAN FOSSILS IN OTHER COUNTRIES. 



701 



Nemertina, MacLeay. 



The Nemertina are white-blooded worms like some of the Hirudina or Leeches. In this group, 

 however, the character of articulation becomes most indistinct. Rudolfi has placed Gordius along 

 with Nemertes (Ent. Syst. 572.) ; and if Gordius goes into the group of Nemertina, it is possible 

 that Filaria may also. Nemertes Borlasii, is a long black sea-worm, which is said to suck Tes- 

 taceous Mollusca. The articulations of its body become visible when it is contracted. If the long 

 vermiform impression in the Cambrian Rocks of Llampeter, Plate 27. f. 4, belong to organic sub- 

 stances, it can only be referred to some animal between Gordius and Nemertes, although probably 

 nearer the former genus. As yet, however, Gordii are only known to occur in fresh water, whereas 

 this fossil production, if it belong to the animal kingdom, was evidently like Nemertes, a native of 

 the sea. 



Genus NEMERTITES ? 



Animal marine, with the linear body, of a Gordius or Filaria. 

 Spec. 1. Nemertites Ollivantii. Murch. n. s.— Plate 27- Fig. 4. 



Postscript. — I have said, that much examination is required to establish accurate comparisons 

 between the Silurian Rocks of England and of other countries. We may, however, observe, 

 that as a certain number of Silurian shells have a wide range in foreign lands, so it may be hoped, 

 that subsequent inquiry will lead to many more identifications. If, indeed, the lists here presented 

 are appealed to, we should say, that the fossils of the Upper Silurian Rocks only, particularly those 

 of the Wenlock formation, had hitherto been much examined by continental authors, since nearly 

 all the forms in their works which we have been able to assimilate to those of our own country, occur 

 in the Upper Silurian group. Thus, while scarcely more than five or six of the Lower Silurian fossils 

 can be compared with published foreign species, we find among the latter a considerable number 

 of Trilobites, Mollusks and Corals, which are common in our Wenlock formation, and a few in the 

 Ludlow Rocks. This comparison is particularly applicable to the Corals : a certain proportion of 

 them have been figured from calcareous rocks in Sweden, Norway and Germany, which are thus 

 placed in direct parallel with the Wenlock limestone. As, however, the fossils of the Upper Ludlow 

 Rock seem to have been little more discovered than those of the Lower Silurian group, are we 

 hence to infer that these fossiliferous deposits, which in England and Wales exhibit transitions or 

 passages from the Silurian system, both in ascending and descending order, are of rare occurrence 

 on the continent, or that the deficiency results from inadequate examination ? Further inquiry can 

 alone determine this point. 



In regard, however, to the diffusion of Silurian deposits over still more distant regions, I may add, 

 that I am more than ever convinced of their existence in Southern Africa. (See p. 585.) Captain (now 

 Sir James) Alexander, whose travels have been referred to, p. 653, has recently laid before me a col- 

 lection of rock specimens collected by himself, and I have no scruple in affirming that the brownish 

 coloured sandstone, which rises to the highest points of the Cedar Mountains, north of the Cape 

 Colony, is a " Lower Silurian'' Rock ; for it is loaded with casts of an Orthis, very closely resem- 

 bling the Orthis callactis, associated with Bellerophon acutus, Tentaculites annulosus, Schloth., and 

 many crinoidal stems, &c. Thus, while the Homalonoti and other fossils found in the ravines and 

 on the slopes of these mountains led me to suppose that they were composed of Upper Silurian 

 Rocks, this fresh importation of specimens in convincing me that the axis of the chain is Lower 



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