1847.] SALTER ON TRINUCLEUS. 253 



by supposing the membrane to collapse at regular intervals, become 

 plicate (5 a), then perforate (5 b), and lastly, separate into linear pro- 

 cesses (5 c) . Now we have in Harpes the flat border, with rows of 

 impressed puncta, which have not yet perforated the fringe. In Ti^i- 

 nucleus JimbriatMs (fig. 4), we have a plicate border, the thin interstices 

 of which have contracted into pores, which is a step beyond the simple 

 perforation in linear series exhibited by T. ornatus, fig. 1 . Lastly, in 

 Ceraurus (Acidaspis, Murch.) we have the structure completed, the 

 linear processes being quite separated into spines. This structure is 

 not anomalous, for the cellular membrane which forms the inner peri- 

 stome of the moss passes through an exactly similar course, becoming, 

 in different species, perforate, in others separated into distinct teeth. 



That these perforate or spinous fringes are not essential, but only 

 supplementary parts of the head, may easily be shown, by the fact 

 that the width of the head, without the fringe, is exactly that of the 

 body, and when the animal is doubled up, the fringe projects freely 

 on all sides. We still require to find anomalous specimens in which 

 all, or some of the above modifications, — plication, perforation, or 

 partially cleft borders, — may be exhibited together, in order to de- 

 monstrate the supposed origin of the structure. 



I now wish to call attention to the species best known to students, 

 the T. Car act act, which the author of the * Silurian System' has taken 

 so much pains to illustrate. And I am sure all naturalists will regret 

 that its classical name must give way to a much older one, by which 

 it has been long knovni on the continent, T. ornatus, Sternberg, 

 described by him in his account of the Prague Museum, 1833. It is 

 not a little singular that foreigners should have adopted the name of 

 Sir Roderick Murchison, without perceiving from his figures that their 

 species was the one he represented. 



The great difficulty of obtaining rare foreign books or specimens 

 is a sufficient reason for the name given in the * Silurian System,' as 

 it was for the naturalists of the day being unwilling to undertake the 

 description of the Trilobites of that work, and for this labour bemg 

 added to Sir Roderick Murchison' s other tasks ; and if our well-known 

 English fossils have to forego their present names, we are in no worse 

 position than our botanists, whose species have been so frequently fore- 

 named on the continent. We may hope for the future that a free 

 interchange of specimens will prevent more of this evil. I would not 

 have said so much, were it not that the T. Caractaci is known as 

 vddely as the * Silurian System,' and even Burmeister, in his late 

 grand work, describes both species without perceiving their identity. A 

 good series of Bohemian Trilobites, now in the possession of the Geol. 

 Survey of Great Britain, has enabled me to set the matter right, and 

 shows too that Barrande has given to our fossil still another name, 

 T. Goldfussii. The T. Bigsbii and T. tessellatus of American na- 

 turaHsts, and T. elongatus and T. latus of Portlock, all belong to the 

 same species, which may be thus characterized : — 



Trin, ornatus. 

 Syn. T. ornatus, Sternb. Verb. Ges. Mus. Prag. 1833, fig. 2 a-, 

 Burm. (Transl. by Ray Soc.) .58. 



VOL. III. — part I. T 



