1933] Whiteaves Description of a Fossil Cyrena. 233 



vision of the Cyrenidae, C. Albertensis may have to be placed in 

 a new genus, but at present it cannot be satisfactorily separated 

 from Cyrena. Unfortunately, the pallial line is not visible in 

 the only specimen of that species that the writer has seen. 



The genus (yrena was constituted by Lamarck in 1818 for 

 the reception oi a number of fresh or brackish water bivalves, 

 with ovately subtrigonal or nearly circular shells and a greenish 

 epidermis, which differ from Unio in their porcellanous or non- 

 nacreous test, and comparatively short lateral hinge teeth. Dr. Paul 

 Fischer, in his Manuel de Conchyliologie, says that there are about 

 80 recent species of Cyrena^ which live in (the warmer parts of) 

 Asia, America and Oceania. On this continent living Cyrenas are 

 not found north of the Southern States. 



In a fossil state, species of Cyretia, as that genus is now un- 

 derstood, are said to range from the Jurassic period up to the 

 present time, and to culminate in the Eocene. The fossil species 

 of Cyrenidae, however, are found much farther to the northward 

 than the living ones have been, the former occurring also in 

 Northern Europe, including the British Islands, and in Canada. 

 Including the one now described, four species of Cyrenidae have 

 so far been recognized as occurring in the Laramie and Belly River 

 formations ot Alberta and Assiniboia. These are Corbicula 

 occidentalis and C. cytheriformis oi Meek and Hay den, Corbicula 

 obligua (nobis), and Cyrena Albertensis. 



Ottawa, Feb. 5, 1903. 



Explanation of Plate IV. 



Fig. I. Cyrena Albertensis. Outline of left valve of the specimen 



described. 



Fig. lA. ,, Dorsal view of the same specimen, slightly 



restored, to show the amount of con- 

 vexity of the two valves when closed. 



