108 THE NAUTILUS. 



charged part is moderately swollen, with the edge remaining 

 sharp. The ova or glochidia form lanceolate, moderately devel- 

 oped placentae. Glochidia almost semicircular, slightly oblique, 

 inequi valve, with one one end somewhat narrower, the other 

 somewhat wider. They are distinctly longer than high. Length 

 0.19; height 0.15 mm. The lower margin is uniformly and 

 broadly rounded, and there is no trace of a point or a hook. 



Color of soft parts (in life) pale, as described previously ; 

 placenta whitish. 



Lastena belongs to the subfamily Union in tie of the family 

 Unionidae, and is most closely allied to Elliptic. This is also 

 supported by the shape of the shell and the beak sculpture. 

 However, Lastena differs from Elliptic (and from all other genera 

 of the Unioninae) by several important characters, which are 

 unique, and would possibly entitle it to the rank of a subfamily, 

 in case the Unioninae should be elevated to a family. In the 

 shell, the most prominent feature is the reduction of the hinge, 

 a case very rarely observed in the Unioninae (the only other one 

 known to me is Gonidea'). In the soft parts, the structure is 

 like Elliptio, but the restriction of the marsupium to the middle 

 part of the other gills is peculiar, and so is the extreme develop- 

 ment of the foot. Also the glochidia, although of the general 

 Unionine type, are unusual on account of their obliquity. 



Lastena represents a unique specialization of the Elliptio-type, 

 and is a very good genus, which, in the systematic arrangement, 

 should follow Elliptio and Uniomerus. 



PUBLICATIONS RECEIVED. 



BULLETINS OF AMERICAN PALEONTOLOGY, No. 24. New and 

 interesting Neocene fossils from the Atlantic Coastal Plain, by 

 Axel Olsson. Numerous new species from the Miocene of Vir- 

 ginia to Florida are described. The blue clay marls of the lower 

 James river valley are considered to belong to the Yorktown 

 formation, and not, as some geologists have stated, to the Calvert. 



