8 BRITISH FOSSIL CRUSTACEA. 
ciently explain the necessity for the commencement of a fresh Monograph, and I am 
happy to state, that, in undertaking it I have received the approval and kind assistance of 
my scientific colleagues, both in the British Museum and in the Museum of Practical 
Geology ; and those gentlemen whose collections can best illustrate the work in hand 
have obligingly opened their museums for my use and reference. My warmest thanks 
are due to Prof. John Phillips, M.A., D.C.L., &c., and Mr. C. Spence Bate, F.R.S., &., 
who, since the meeting of the British Association at Bath in 1864, have willingly aided 
me in my researches in the British Fossil Crustacea. 
All assistance received will, I trust, be found duly acknowledged in its proper place. 
The present part forms only the first chapter of the history of the MZerostomata, but it 
has been considered desirable to issue this instalment on account of the number of plates 
needed to illustrate the entire group, and the consequent delay caused by their pre- 
paration. 
CLASSIFICATION OF THE MEROSTOMATA.* 
I have experienced considerable difficulty in proposing a classification for this remark- 
able group that may appear to differ to any extent from the conclusions of the eminent 
zoologists who have preceded me in this work; but having the advantage not only of 
being able to consult and compare their published labours, but also of examining 
numerous specimens in a far better state of preservation than any hitherto examined 
or described in this country, I venture to hope that the following arrangement—with such 
modifications as may be deemed needful during the publication of the remaining parts 
of this Monograph—will be found to accord, not only with the general and detailed 
structure of the group and their family relationships, but also as an appropriately framed 
order of the great. Crustacean class. 
1 This name (derived from pnpés, a thigh, and oropa, a mouth) was proposed by Dr. J. D. Dana in 
his great work on the Crustacea (1852) already quoted, but is adopted here for a much larger group than 
was contemplated by him. I prefer to enlarge a group proposed by so eminent a carcinologist, to the 
alternative of introducing a fresh name or the adoption of one which, though older, is inappropriate, 
having been founded upon an incorrect view of the structure of the fossil forms it included. (See p. 24, 
paragraphs 28 and 33.) 
