78 



OBSERVATIONS. 



Inhabits the Black Warrior and Alabama rivers, 

 Avhere I found it in abundance; also the Ohio and its 

 tributaries. 



The ovate form of this species and its obliquity 

 will distinguish it at a glance from undatus, Barnes. 

 The young is remarkable for being of yellow colour 

 behind the umbonial slope, which soon disappears in 

 general as the shell increases in size. 



Mr. Lea appears to be ignorant of the true distinc- 

 tive character of this species, since he affirms that I 

 have published it under the name of mytiloides; the 

 latter is destitute of the callosity of the cardinal plate 

 which characterizes the obligims, has a very different 

 lunule, and is dissimilar in outline to that species. 

 Those who are conversant with the two shells will 

 not confound them. 



Mr. Lea considers the obliqua of Lamarck to be 

 identical with undatus of Barnes, but Lamarck's de- 

 scription is wholly inapplicable to the latter, whilst 

 it agrees with the cbenus of Lea, with which it is 

 identical, according to Ferussac. 



UNIO APICULATUS. 



Plate XLIV.— Fig. 1. 

 DESCRIPTION. 



Shell subquadrate, compressed; summits not very 

 prominent; hinge margin declining; disks with a dilat- 

 ed not deeply impressed furrow; umbonial slope 



