274 THE JOURNAL OF GEOLOGY. 



able as yet to offer any satisfactory explanation," can be, since it 

 terminates before it reaches the point of the scicula, nothing else 

 than that portion of the virgula which lies in the wall of the 

 scicula. 



Tornquist nowhere says that the described species are mono- 

 prionidian, but this can be clearly seen in the figures 39-41 of 

 Cephalograptits cometa, Gein., and if those just cited are compared 

 with my own, there can be no doubt that the species above men- 

 tioned are also monoprionidian. 



It is particularly interesting to note that the presence of a 

 longitudinal septum does not depend on the diprionidian charac- 

 ter of the DiplograptidcB as generall}^ accepted. 



EXPLANATION OF PLATE. 



The figures have been drawn about twice the size of the scale, with Zeiss 

 and Abbe's drawing apparatus. The shading was obtained by still greater 

 enlargement, and by various accessories to the microscope. The given scale 

 does not apply to figure 10. 



Fig. I. Young scicula ; dorsal side. X 37. 



Figs. 2-3. Adult scicula ; front view. The thecse are removed. 37-1. 



Fig. 4. Form and place of the first theca and the perforation from which 

 the second will come ; front view. X 37. 



Fig. 5. The same; dorsal view. X 37. 



Fig. 6. The first theca with three spines, two of which are united by a 

 thin skin. X 37. 



Fig. 7. Form and position of the second and third theca2 ; front view. X 37. 



Fig. 8. Form and position of the fourth theca and imbedded scicula. X 37. 



Fig. g. Incorporation of the scicula in the hydrosoma. X 37. 



Fig. 10. Distal portion. The transparency partially made use of. The 

 virgula is wholly free. X 13. 



Figs. 11-12. Attachment of the proximal edges of the partitions to the 

 virgula. X 37. 



The material is in the collection of the Geological Institute at Upsala. 



Carl Wiman. 



