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basal portion the conical spicules are seen converging to the central axis. The 



spicules of the upper portion are too minute to be represented in the figure. 



Prom Silurian strata of Upper Ludlow age, Pentland Hills, near Edinburgh . . 154 

 Fi"'. 12(7. The same. Natural size. A smaller and narrower example from the same 



locality. This and the preceding figure are drawn from specimens loaned by 



Dr. H. Traquair, F.R.S. 

 Fig. 12 6. The same. Natural size. An average-sized specimen. Drawn from an example 



in the collection of Prof. H. A. Nicholson. 

 Fi"'. 12 c. The same. A portion of the interior of the upper part of a specimen, enlarged 



ten times, showing the disposition of the spicules. Only casts of the spicules 



are preserved. 

 Fi"-. 12 d. The same. A natural cast of a detached conical spicule from the basal portion 



of the sponge. Enlarged ten times. 

 Fig. 12 e. The same. Natural casts of detached five- and possibly six-rayed spicules 



belonging to the upper portion of the sponge. Enlarged fifteen times. 



