Baker — Some Interesting Molluscan Monstrosities. 145 



pearly matter, evidently to cover some foreign substance which 

 found entrance between the valve and the mantle of the 

 animal. The additional material is confined to the region 

 bounded by the muscle scars, and the pallial line and hinge. 

 A part of the posterior adductor muscle (posterior end) is 

 covered by a thick callus, and the anterior adductor muscle 

 scar is strengthened by the addition of numerous pearly 

 pustules. 



Length, 106.00; height, 63.00 ; the thickness of one valve 

 15.00 mill. 



Weight of a normal valve of same size 2.45 oz. 



Weight of abnormal valve 3.75 oz. 



Unio gibbosus Barnes. 



PI. XI. f. 2,4. 



Monstrosities apparently occur in this species more than in 

 any other, it seeming to be especially susceptible to abnor- 

 malities. One specimen (fig. 2) has the shell twisted 

 on the hinge line, causing the anterior end of the right 

 valve to be depressed below that of the left valve. The 

 latter has a depression which extends from the umbo to the 

 ventral margin and there is a corresponding swelling in the 

 right valve. The right valve has two lateral teeth or laminae, 

 one about 12 mill, long, smooth, extending a short distance 

 behind the cardinal teeth and the normal lamina, which is 

 triangular and very rough. The teeth of the left valve appear 

 to be normal. Interior of shell white. 



Length 88.50 ; height 42.00; breadth 33.50 mill. 



Another specimen of this species (fig. 4) has the posterior 

 basal portion produced as in the females of some species of 

 Lampsilis. The nacre of this specimen is a beautiful mauve 

 or purple. 



Several Unios recently collected bear patches of pearly 

 secretions resembling little piles of agglutinated sand, and 

 indeed these without doubt are small grains of sand covered 

 with pearly matter. These masses are placed in different 

 parts of the shell, some being outside of the pallial line, some 

 near the cavity of the beaks and others near the adductor 

 muscles. The specimens figured were collected by Mr. Joseph 

 Kinstler in the Mississippi River, while pearl hunting. 



