PLATE IV.

ORTHIS VANUXEMI.

Page 73.

Fig. 1. Vertical longitudinal section through a portion of the test, showing the laminæ of the shell and tubuli. Some of the tubuli bifur

cate before reaching the surface.

Fig. 2. Vertical longitudinal section through the front of two valves, showing very distinctly the oblique laminæ and the size of the vertical tubuli.

Fig. 3. Horizontal section from near the surface, showing large and small

punctæ.

Fig. 4. Section from near the center of a valve, showing the fibrous and punctate structure.

Fig. 5. Section at some depth below the surface, showing the regular rows of punctæ and flexuous direction of the fibres which run independently of the rows of punctæ.

ORTHIS PENELOPE.

Page 73.

Fig. 6. Horizontal section showing the very strongly marked rows of punctæ and intermediate fibrous structure.

SCHIZOPHORIA MULTISTRIATA.

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Fig. 7. Showing the numerous minute punctæ and fibrous structure of the shell of this species.

SCHIZOPHORIA IOWENSIS.

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Fig. 8. A section from near the surface, showing the numerous punctæ. In sections cut at a greater depth the appearance is similar in general features to fig. 9.

SCHIZOPHORIA TULLIENSIS.

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Fig. 9. Showing the numerous close puncta with no definite arrangement.

SCHIZOPHORIA IMPRESSA.

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Fig. 10. Section from nearer the surface than the preceding, showing the broad bands of puncta which gradually coalesce and produce an evenly punctate structure.