TABLE OF CONTENTS. 



Page 



PREPACK Hi 



INTRODUCTION vii 



I. THE GENUS PISIDIUM 1 



11. HISTORY OF THE BRITISH SPECIES 6 



III. LlST OF INDETERMINATE P\L2E ARCTIC FORMS 13 



IV. DESCRIPTIONS OF THE SPECIES RECOGNIZED 16 



1. Pisidium amnicum (Miiller) 16 



2. astartoides, Sandb 27 



.'>. casertanum (Poll) 31 



4. nitidum, Jenyns 44 



5. personatiim. Malm 53 



6. pusittum (Gmelin) Jenyns 60 



7. ,, inilium, Held 70 



8. pulchellum, Jenyns 78 



'>. ,, ntbtnatcatum, Malm 84 



10. hemlmoanum (Shepp.) , 93 



11. supinum, A. Schmidt ,100 



12. ,, parvulum, Clessin 105 



13. steenbuchii (Miiller) . 107 



14. lilljeborgii, Clessin , ... Ill 



15. hibernicum, Westld 116 



16. obtusale (Lam. ?) Jenyns 119 



17. vincentianum, B. B. \Voodw 127 



V. BIBLIOGRAPHY ' 129 



VI. INDEX 141 



PLATES I-XXX. WITH THEIR EXPLANATIONS. 



TEXT FIGURE. 



Page 

 TOPOGRAPHY OF THE HINGE OF PISIDICM . 3 



