102 Anniversary Address to the 
lipsocephalus, Sao, Arionellus, Hydrocephalus, and Agnos- 
tus. 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 assemblages 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 Linnzus. 
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 Olenoid family of Trilobites, al- 
most 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 imme- 
diately above. The same, or a very similar distribution, has 
been observed of late years by Angelin, 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 Professor Sedgwick, who recognised 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 resumé on the Lower Paleozoics of N. Wales, com- 
municated 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 M. Salter goes to 
support the stress laid upon them by M. Barrande. In 
the prosecution of the search, a further result has been ob- 
