89 



Figures. 



Anodonta cygnea. PI. P. Shell, with animal, showing the fringed si- 

 phonal orifices and protruded tongue-like foot. 



Anodonta angulata. PI. 31. Pig. 180. Shell of a peculiar trapeziform 

 shape, showing the toothless ligamentary hinge. 



Genus 4. IRIDINA, Lamarck. 



Animal ; similar to that of Unio, with the posterior orifices pro- 

 longed into two short unequal siphonal tubes. 



Shell ; ovate or elongated, with the hinge toothless, but crenately 

 tubercled. 



As in Hyria, the posterior orifices of the animal of Iridina are prolonged 

 into two short unequal siphons. The shell is not so thin as in Anodonta, 

 but it is never massive as in Unio ; the hinge is, nevertheless, toothless. 

 In the place of teeth a number of crenated tubercles are formed along 

 the hinge margin, and in the species we have selected for illustration they 

 are developed very largely and wrinkle-like. 



The Iridina do not consort either with the Unios or Anodons. They are 

 all natives of Africa, living abundantly in the Nile along with another genus 

 peculiar to that habitat, Galathcea radiata. The shells are used, says the 

 African traveller M. Cailliaud, by the natives of Lower Egypt in preparing 

 flax, and also as spoons for measuring oil, butter, and different kinds of 

 provisions. The latest discovered species, /. Spekii, was collected by 

 Captain Speke in the great freshwater Lake Tanganyika in Central Africa. 

 It is of the same type as I. ovata, selected by Conrad as the type of a 

 genus with the name of Pleiodon. 



1. cselestis, Lea. 



2. dubia, id. 



3. exotica, Lam. 



Species. 



4. Leaii, Sow. 



5. ovata, Swain. 



6. rubens, Lam. 



7. Spekii, Woodw. 



8. valens, Parr. 



9. Walbergi, Krauss. 



Figure. 



Iridina ovata. PI. 33. Pig. 184. Shell, with a valve dropped to show 

 the crenately tubercled hinge. 



VOL. II. 



