8 Dr. U. A. Nicholson on the Oenus Stromatopora. 



are somewhat cup-shaped ; and others, again, have the form 

 of irregular and extended crusts, apparently attached at one 

 point to some solid body, from which they spread laterally in 

 every direction, or seem to form incrusting sheets. 



Upon the whole, I think the evidence is very decidedly in 

 favour of the view that the genus Stromato2Jora is referable to 

 the Calcispongiffi. In accordance with this view, I retain in 

 this genus the forms which I have named S. tuberculata, S. gra- 

 nulata, S. perforata, and S. Hindei, since these are undoubted 

 sponges, and would upon any other view of the affinities of 

 /Stromatopora require to have a new genus formed for their 

 reception. 



1. Stromatopora tuberculata, Nicholson. 



Stro?natopora tuberculata, Nicholson, Ann. & Mag. Nat. Hist., Aug. 

 1873, pi. iv. figs. 2, 2 a. 



Having now obtained a considerable number of additional 

 specimens of this species, I have to add two observations of 

 importance to my original description. In the first place, I 

 have now obtained specimens showing that the under surface 

 of the expansions of S. tuhercidata is covered by a thin calca- 

 reous basement-layer, which is thrown into very immcrous 

 concentrically arranged undulating wrinkles. This sm'face 

 thus presents somewhat the appearance of the epitheca of a 

 Favosites ; but it is much thinner and rougher, and is pierced 

 by apertures. In the second place, both the upper and the lower 

 surface exhibit at irregular intervals rounded apertures which 

 are placed at distances apart of from two lines to half an inch, 

 and have a diameter of from half a line to two-thirds of a line. 

 These apertures are wanting in some specimens, which, how- 

 ever, are but fragmentary, whilst they can readily be detected 

 in others. They are the openings of canals which penetrate 

 the mass in a more or less vertical direction ; and I noticed 

 their occurrence in my original description of the species, 

 though I did not at that time fully recognize their nature. 

 The case w^as thus stated by me : — " Many examples exhibit 

 rounded openings or tubes, from half a line to a line in dia- 

 meter, descending at right angles to the mass, and placed at 

 varying intervals. These openings are not elevated above the 

 general surface. They are not constant in their occurrence, 

 though very generally present ; and I have not been able to 

 satisfy myself that they are not truly extraneous to the fossil. 

 They may, perhaps, be annelidous in their nature; or they 

 may be due to the fact that the organism has enveloped a 

 colony of Syringopora, which has subsequently been dis- 



