ANNIVERSARY ADDRESS OF THE PRESIDENT. XXXI 



The third stage of his Lower Silurian, and the first of his fossili- 

 ferous horizons, includes his " Schiste protozoique," and attains a 

 thickness of 1200 feet. It contains no beds of limestone. The 

 fauna of this section is very peculiar ; it is composed almost totally 

 of Trilobites, the other fossils being a Pteropod, some Cystidese, and 

 an Orthis. These constitute an assemblage upon which he lays 

 great stress and designates primordial. All its species, without 

 exception, are peculiar to itself, and of the Trilobites, all the genera 

 are so, with the exception of Agnostus. The peculiar genera are 

 either low and rudimentary types, or members of the Glenoid or 

 Calymenoid families ; not typical or highly developed fonns. They 

 are Paradoxides, Conocephalus, Ellipsocephalus, Sao, Arionellus, 

 Hydrocephalus, and Agnostus. Of the first of these genera there 

 are no fewer than twelve species, some of them exceedingly prolific. 

 These primordial Trilobites have a peculiar facies of their own, de- 

 pendent on the multiplication of their thoracic segments, and the 

 diminution of their caudal shield or pygidium. M. Barrande compares 

 this primordial fauna of Bohemia with certain fossiliferous assem- 

 blages similarly placed at the base of the fossiliferous Silurians in 

 Wales, Norway, and Sweden, in which last country, indeed, the 

 peculiarities of its fossils long ago attracted the attention of naturalists 

 and the notice of Linnseus. 



The isolation of this primordial zone, as distinguished from the 

 mass of the Lower Silurian, is chiefly maintained by the grouping in 

 it of the Glenoid family of Trilobites, almost to the exclusion of all 

 others. It is not quite certain that more than one of the genera of 

 Trilobites distinctive of this zone are found in any higher beds. The 

 exception is Agnostus, the lowest and most rudimentary type of its 

 tribe. Yet even this has its metropolis in the primordial zone, and 

 sends but a few stragglers into the division immediately above. 

 The same, or a very similar distribution, has been observed of late 

 years by Angelui, who during 1852 commenced illustrating the fauna 

 of the Swedish rocks. 



In Wales the existence of this primordial fauna has been clearly 

 made out. The rocks which contain it are those designated by Pro- 

 fessor Sedgwick, who recognized their importance, as the " Lingula 

 beds," a name adopted by the Geological Survey. Fossils were first 

 I believe, found in them by Mr. Davis, who discovered the Lingula, 

 from which they received this name. They have been thoroughly 

 examined by my colleagues of the Geological Survey, and are stated 

 in the resume on the Lower Palaeozoics of N. Wales, communicated 

 by Professor Ramsay to the Society last April, to be about 7000 feet 

 thick. Their importance has been fully recognized for some time by 

 the surveyors, and the additional evidence accumulated last autumn 

 by Mr. Salter goes to support the stress laid upon them by M. Bar- 

 rande. In the prosecution of the search, a further result has been 

 obtained in the way of a subdivision of the group, and a palseontolo- 

 gical distinction of importance has been indicated. They prove capable 

 of division into two well-marked sections, viz. a lower, of which 

 Agnostus (probably the identical species described from the alum 



