A MONOGEAPH 



OF 



THE CARBONIFEROUS BIVALVE ENTOMOSTRACA 



OF 



GREAT BRITAIN AND IRELAND. 



PART I.-THE CYPMDINAD.^: AND ALLIED GROUPS. 



INTRODUCTION. 



The classification of the very numerous Bivalved Entomostraca found in the Car- 

 boniferous Limestones, Shales, and Ironstones, and submitted to our examination by 

 numerous friends and correspondents, has been no easy task. Much as, at first sight, 

 the fossil oval carapace-valves, notched on the anterior edge, may resemble some of the 

 existing Cypridinadcs , we have to recollect that, even among the latter, generic discrimi- 

 nation by means of the shell (test or bivalved carapace) is almost impossible. So great is 

 the modification of the shape of valves in any one group, and so little is the persistency 

 among them of any one feature or character, or any set of features, that, except in a very 

 general manner, we may not even take either the "notch" or the contour as a guide, 

 not knowing the soft parts of the animal, remarkable as the similarity may sometimes 

 be between the old and the modern shells. 



It is impossible to group many even of the recent " notched " forms under the genus 

 Cypridina, in accordance with the requirements of natural classification, by regarding 

 only one character; for from the limbs and other organs are taken the main features 

 of distinction between Cypridina, Philomedes, Brady cinetiis, and Asterope, all formerly 

 groupe'd as CypridincB. Evidently, therefore, we cannot say for certain that the 

 extremely old Cypridinadce of the Carboniferous Period, which preceded those of our 

 day by countless generations, susceptible of numberless variations, are generically the same 

 as those now living. 



To escape this difficulty, and not to fall into error, we once thought of adopting such a 

 term as " Cypridinopsis " for all these Cypridina-like forms, whether really allied to one 

 more than to another of the genera above alluded to — relationships which the absence of 

 the limbs prevents us from defining with exactness. But several subgeneric terms 



A 



