PRELIMINARY OBSERVATIONS. 3 
‘Report on the Geology of the County of Londonderry, and of parts of Tyrone and 
Fermanagh.’ 
In 1846, Prof. M‘Coy, in his work, ‘A Synopsis of the Silurian Fossils of Ireland,’ 
described some ninety species, and of these he figured thirty-three ; but this work, as well 
as those already mentioned and those to be hereafter referred to, will require considerable 
revision as far as the determination or identification of the species is concerned ; for, as 
science progresses, our knowledge becomes extended and improved, and we are con- 
sequently better able to discover and appreciate those characters which separate one species 
from another. 
In 1847-48, in the ‘ London Geological Journal,’ and in the ‘ Bulletin de la Société 
Géologique de France,’ I described and figured some seventy-eight of our British Upper 
Silurian species, which I had myself in a great measure collected in some of Murchison’s 
typical Silurian localities. 
In 1848, in the second volume of the ‘Memoirs of the Geological Survey of Great 
Britain, Prof. Phillips and Mr. Salter described and illustrated a small number of 
Silurian Brachiopoda. 
In 1852, in the second fasciculus of his important work on ‘British Palaeozoic 
Fossils,’ Prof. M‘Coy described in great minuteness one hundred and eighteen species or 
varieties of Lower Paleozoic Brachiopoda; but of these he figured only twenty-five. It 
is much to be regretted, that a larger number of the fossils had not been illustrated, for 
a good figure is very often more valuable than the most elaborate description; and 
especially so, when forms vary so slightly one from another that it is at times hardly 
possible to adequately express with words small differences which the figure at once con- 
veys to the eye of the experienced observer. 
In 1854, in his revised ‘Catalogue of British Fossils,’ Prof. Morris enumerates 
some one hundred and seventy species or varieties ; and in the last edition of ‘ Siluria,’ 
published in 1859, Mr. Salter furnishes us with a list of one hundred and seventy-seven 
species of Brachiopoda, which he distributes in the various stratigraphical groups or 
divisions adopted by Sir R. Murchison in this his last-named very important work. In 
this edition are likewise added, in the shape of woodcuts, figures of several species of 
Brachiopoda which had not been discovered at the time the original ‘ Silurian System’ 
was being printed. We must also notice that in ‘The Geologist’ for 1859, Prof. Morris 
published a list of British Silurian Fossils, including Brachiopoda, “ Stratigraphically 
and Zoologically arranged, with a Reference to a Figure of each Species.” To this 
paper is also appended a long list of books and memoirs relating to Silurian and 
Cambrian rocks and fossils. 
In 1866, in the third volume of the ‘Memoirs of the Geological Survey,’ Mr. Salter 
describes and figures several species of Brachiopoda, in the “ Appendix ” to Prof. Ramsay’s 
“ Geology of North Wales.” 
Moreover, a few species of British Silurian Brachiopoda have been referred to in various 
