Four years have elapsed since I first commenced my researches among the Carboniferous Brachiopoda of Great Britain ; and I should certainly by this time have completed my task, had not the unfortunate delay in the publication of the last two or three volumes of the Palæontographical Society induced me to undertake other work which would not require to lie printed and unpublished for upwards of one year and a half. My monograph cannot, consequently, be completed or entirely published for some time to come, perhaps a year or more; but as my researches in connection with the subject are almost ended, since the whole series of species at present known have been as carefully examined as my means and materials would permit, it may, perhaps, be as well that I should at once expose the results of my laborious enquiry, in the hope that by so doing some further assistance and advice may be proffered; which might enable me to make the monograph still more complete, and at the same time admit of my correcting in the concluding pages those unavoidable mistakes which have been commited during the interval which has elapsed since the commencement of its publication.

It may be thought by some while perusing the accompanying catalogue that the work to be gone through was but small in comparison with the time employed, but such would be an erroneous assumption, and a sad return to the numerous friends in England, Scotland, and Ireland, who have so zealously afforded their valuable and valued assistance, by incessantly ransacking the country in order to obtain every possible specimen that might assist and tend to complete the history of British Carboniferous species.