108 Transactions of fhe Society . 



diaphanous elastic curtains in some cases; although of such a 

 diaphanous nature the crown of the test of C.fiava (Greet!) Penan 1 

 is studded with small particles of extraneous materials affixed to 

 its outer surface, and in the case of C.fiava var. coronata (Penard) 

 Wailes, has a projecting ring or circular fold of membrane around 

 the crown of the test ; whilst C. aculeata (Greeff) Averintzeff has 

 a circlet of stout spines. 



The tests of most species of Arcclla appear punctate under a 

 low power, but a higher magnification gives them the appearance 

 of being formed of circular or hexagonal disks cemented together 

 (IT. Ill, fig. 1). Penard (4), with his usual accuracy, shows that 

 the test of A. vulgaris Ehrenb. consists of a thin chitinous plate 

 covered on one side with a network of low ribs forming shallow 

 hexagonal cells, the free edges of these ribs becoming thickened, 

 this thickening increasing with the age of the animal, until from 

 a girder-like section they eventually coalesce at their free edges, 

 and the fully mature test finally consists of two plates joined 

 together by a network of ribs, and it is owing to the spaces 

 between them as seen through the translucent plates or coverings 

 that the tests have a punctate appearance. As the tests are only 



EXPLANATION OP PLATE III. 



Eig. 1. — Surface of portion of an Arcella test, x about 2500. 

 ,, 2-4. — Section of the same. 2. When immature. 3. When older. 4. Mature 



test, x about 2500. 

 ,, 5. — Section of test of Arcella artocrea Leidy, through " pores " around the 



aperture, x 2000. 

 ,, 6. — Silicious elements of test of Nebela griseola Penard. x about 800. 



,, 7, 8. — Portions of test of N. vitrsea Penard. x 1000. (After Penard.) 

 ,, 9. — Side view of aperture of Euglypha ciliata Ehrenb. x 1000. 



„ 10. — Body-scale of E. crenulata Wailes. x 1000. 

 „ 11. — Ditto of E. crenulata var. minor Wailes. x 1000. 

 ,, 12. — Aperture-scales of E. alveolata Dujardin. x 1000. 



13. Ditto of E. Ixvts Perty. x 1000. 



14. Ditto of E. rotunda Wailes. x 3000. 

 „ 15. Ditto of E. crenulata Wailes. x 1000. 

 ,, 16. Ditto of E. compressa Carter. X 1000. 



,, 17. — Portion of test of Nebela scutellata Wailes, showing the small strength- 

 ening plates over the joints of the larger plates, x 1000. 



,, 18. -Spine-scale of Euglypha crenulata Wailes. x 800. 



„ 19-24. — Spines of various forms of E. compressa Carter, x 1000. 23. Normal 

 form. 20, 22. Narrow edge views. 



,, 25, 26. — Apex of test of E. mucronata Leidy. x 1000. 25. Narrow view. 

 26. Broad view. 



,, 27-29. — Portions of tests of Gyphoderia ampulla Ehrenb. x 2000. 



,, 30. — Portion of a test of the same, x 4000. 



,, 31. Ditto ditto of C. ampulla var. major Penard ; a rare form from 

 Yorkshire, x 2000. 



,, 32, 83. — Portion of a normal test of the same variety, showing test in 

 section (32), and a portion of the surface with a line of fracture (33). 

 X 4000. 



,, 34-36. — Portions of two tests of C. trochus var. amphoralis Wailes, and 

 section (35). x 2000. 



