SOME INDIAN FRESHWATER SHELLS. 99 



PELECYPODA. 



Unionise. 



Shells of this family are regular, equivalve, closed. A nacreous structure. 

 Penostracum often thick. An external ligament large. Well developed hinge 

 teeth. 



Animal with mantle margins united between siphonal orifices. Organ of 

 locomotion, the " foot ", large. Sexes distinct. Of universal distribution in 

 lakes, ponds and rivers. 



Onto corrugatus (Smith). 



Shell. — Roundish tapering towards anterior. Hinge thick and prominent. 

 Outside of shell thick and olive brown, sometimes greenish. Umbo often 

 eroded. Interior white with iridescent hues. Hinge teeth large and thick. 



Length.— 48". 



V. ceeruleus (Lea). 



Shell. — Somewhat oval, lengthened. Hinge not so pronounced as in the last. 

 Teeth small. In colour this species varies. Some I have are externally olive 

 yellow, others again are a beautiful bluish green. Interior bluish white. 



Length. — 56*5. I have specimens from Tirhoot, Cachar and Delhi. 



U. flavidens (Bens). 



Shell.— Oval, thick, hinge well developed. Whole shell very thick. Exterior 

 a mixture of brown green and yellow. Interior of shell yellow in some, 

 salmon-pink in others. Hinge teeth thick. Posterior teeth serrated. Aductor 

 scars very pronounced. Umbo as a rule eroded. 



Length.— £2*5. I have specimens from Calcutta, Tirhoot and Cachar. 



U. marginaUs (Lk). 



Shell .—When adult large, oval. Hinge large and thick. Exterior a brownish 

 black in some specimens, olive brown in others. Hinge teeth large and very 

 iridescent. Posterior teeth thick and finely serrated. Whole interior surface 

 very iridescent. In a number of specimens I have examined they all show 

 small pearly outgrowths towards anterior. One specimen I bave, given me by 

 Capt. Peile and collected at Poona, the whole inside of the shell is orange 

 yellow. 



Length. — 86 to 96. I have specimens from Calcutta, Poona, Cachar and 

 Tirhoot. 



U. lamellatus (Lea). 



Shell.— Thm. Teeth small. Exterior olive brown. Interior very iridescent. 



Length. — 83. 



U. sikhimensis (Lea). 



Shell —Somewhat oval. Hinge very well developed. Exterior greenish and 

 olive brown. Posterior teeth well developed. Interior bluish white. 



Length. — 36 - 5. 



U. crispisulcatus (Bens). 



Size small. Exterior very much serrated. 



