1869.] GEOLOGY AND MINERALOGY. 341 



Fossil carapaces of Cladocera have not been recognised, their 

 extreme tenuity probably being neither favorable for their pre- 

 servation uor, if preserved, to their detection in the fossil state. 



The Bivalved Phyllopods, such as Limnadia, Ustheria, and 

 Limnetis, are larger than the Cladocera, and their valves are 

 usually thicker and stronger. In shape round, oval, or oblong, 

 they often resemble the shells of Conchifera or Bivalved Molluscs, 

 and have been mistaken for them when living, and much more 

 frequently in the fossil condition. The presence of a straight 

 hinge-line, of umbones, and of concentric lines of growth, are 

 special features in which they more or less imitate the Conchifera, 

 such as Avicida, Telliaa, Pisidium, &c. Estheria donadformis 

 came to the British Museum as a Nucula ; but Dr. Baird re- 

 cognised its crustacean characters, disguised as they are by the 

 moUuscan shape. Estheria minuia long passed as a little shell 

 among geologists until Wrof. Quekett's microscope detected the 

 hexagonal cell-tissue of the Crustacean in fragments of the fossil : 

 see my ' Monograph of the Fossil Estheriae ' (Palaeontographical 

 Society), 1862, pages 3, 11, &c. 



Very different kinds of carapace-valves belong to the Oslracoda. 

 A synopsis of the recent British forms of this great group, care- 

 fully drawn up and illustrated by Mr. G. S. Brady in the 

 ' Intellectual Observer ' for September, 1867, gives us a good 

 general view of these very interesting Bivalved Entomonstraca, 

 amongst which are (excepting some of the Copepoda and Cla- 

 docera) the most common of the marine and freshwater forms, 

 both recent and fossil. Thus — 



Cyprid^. — Cypris ; Cypridopsis; Paracypris ; Nbtodromas ; 

 Candona ; Pontocypris ; Bairdia ; Macrocypris. 



Cytherid^. — Cythere (and Cythereis) ; Limnocy there ; 

 Cytheridea (and Cyprideis); Cytheropsis (to be changed to 

 "Eucythere") Hyohates ; Loxoconcha (^Normania); Xesto- 

 leberis ; Cytherura ; Gytheropteron ; Bythocythere ; Psmdo- 

 cythere ; Cytherideis ; Sderochilus : Paradoxostoma. 



GYPRlBimDJE.— (Cypridina ,) Philomedes ; CyUndoleheris ; 

 Bradycinetus. 



Conch (ECIAD^. — Conchoeda. 



PoLYCOPiD^. — Polycope. 



Cytherellid^. — Cytherella. 



The valves of the Gypridai (Brady) are small, usually either 

 kidney-shaped, oblong, or boat-shaped, smooth or bearing only 



