119 



EXPLANATION OF THE PLATES. 



PLATE I. 



Fig. 1. Surirella Venus, weakly magnified. Natural 



length of the cuirass: 0,002565. Breadth: 



0,000104 of an inch (Paris). 

 2. Seen from above, more magnified. 

 3. Open animalcule. 

 4. Another, equally open 5 a. the cuirass ; b. its 



inge; c. the white and transparent coat 5 d. 



incision, in the internal membrane 5 e. the 



brown or green content. 

 4. A. Ribs and furrows B. on the edge of the 



cuirass. 

 5. Navicula ciliata, two united animalcules. Length 



of the cuirass : 0,00044. 

 6. Separated animalcule, sidewise seen. 

 7. The same, seen from backwards 5 a. cuirass 



with angles and hairs 5 b. edge of the pedal 



surface 5 c. extremities of the sides 5 d. d. 



orifices of the alimentary tubes. 

 8. The same animalcule, seen from the pedal 



surface 5 e. d. d. orifices of the two alimentary 



tubes seen sidewise. 

 9. Kavicula costata , seen sidewise 5 length: 



0,00226. 

 10. The same, seen from downwards ; a. cuirass ; 



b. the brown content 5 b * b x , pedal bladders 5 



f. f. intestinal tubes, and their orifices 5 d. 



ombilic of the middle ribs. 

 11. Two united animalcules. 



12. Frustulia appendiculala ; two united animal- 

 cules. Length: 0,00139 5 breadth: 0,00055. 



