EXPLANATIONS OP PLATE XVIIL 



Dendrograptus? (Callograptus?) diffusus, page 132. 



Fig. 1. A portion of a broken frond from near the base. The test is removed in some 

 parts, showing celluliferous markings. 

 " 2. A fragment of another specimen with similar cell-markings. 

 " 3. An enlargement, showing the cell-apertures. The specimens are extremely 

 compressed. 



Callograptus elegans, page 134. 



Fig. 4. A fragment which is more lax and spreading, with shorter branchlets 

 than the ordinary specimens, but having similar stria;, and a similar arrange- 

 ment of cellules. 



Dendrograptus gracilis, page 132. 



Fig. 5. Two of the larger branches with their sub-divisions, of the natural size. 



' 6. An enlargement from one of the branchlets, showing the striate surface and 

 the deep indentation of the cellules. 



