22 EXPLANATION OF THE PLATES. 



elongatum, at the period of its perfect developement. 

 Fig. 4. The same in a younger condition. Fig. 6. The 

 same with the frustules thrown back. Fig. 5. The same, 

 var. cuneatum. — Figs. 7 and 8. States of Diatoma virescens ? 

 — Fig. 9. Tabellaria Jlocculosum, in an early period of its 

 growth. Fig. 10. The same in a more advanced period 

 of its developement. 



PLATE XCV. 



Fig. 1. Fragilaria pectbialis, showing the stria on the anterior 

 surface of the frustules. Fig. 2. The same. Fig. 3. 

 Showing the oblique division of the frustules which occa- 

 sionally takes place. Fig. 4. An interesting condition of 

 the same : a a, end view of frustules of the species in its 

 ordinary state: b, the same of frustules of the variety 

 /3 undulata. — Fig. 5. Filaments of Fragilaria hyemalis : a, 

 front view ; b, end view of frustules of the same. — Fig. 6. 

 Fragilaria rhabdosoma: a, front view; b,end view. — Figs. 7 

 and 8. Successive stages of the developement of Diatoma 

 virescens : a a a, front views ; b b, end views of frustules of 

 the same. 



PLATE XCVI. 



Figs. 1 to 4. Portions of Meridion circulare of different ages. 

 Fig. 5. Frustules of a condition of the same. Fig. 6. : a a, 

 front view of two frustules of the same : b b, side view of 

 the same. — Figs. 7 and 8. Fronds of Meridion constriction. 

 Fig. 9. : a c, front view of two frustules of the same : b d, 

 end view of the same. — Fig. 10. Tabellaria fenestratum : 

 a, front view ; b, end view of a frustule of the same. — 

 Fig. 1 1 . Tabellaria Jlocculosum in the most advanced stage 

 of its developement : a front view ; b, end view of a frus- 

 tule of the same. 



PLATE XCVII. 



Fig, 1. Exilaria capitata. — Fig. 2. Exilaria Ulna. — Fig. 3. 

 Exilaria fasciculata. — Fig. 4. Exilaria lunaris. — - Fig. 5. 



