Dr. II. A. Nicholson on the Genus Stromatopora. 13 



tava are sometimes connected by transverse pillars, but more 

 commonly they are so bent and cm-ved as to inosculate with 

 one another at points closely approximated, thus giving the 

 whole mass a vesicular structure. Well preserved specimens 

 show about eight laminfe in the space of one line. The upper 

 surface of the fossil exhibits not only the linear and vermicular 

 openings above spoken of as produced by the interlaminar 

 spaces, but also a scries of large rounded or oval openings, 

 which are more or less irregularly disposed, and which are 

 the orifices of so many canals which penetrate the mass verti- 

 cally or obliquely. The size of these oscular apertures varies ; 

 but most of them have a diameter of from a line to a line 

 and a half. They also vary greatly in their number in a given 

 space, some fragments exhibiting many of them placed close 

 together, whilst others only show a few, and these remote. 

 The walls of the canals leading away from these openings are 

 not lined by a continuous calcareous membrane (as in S. per- 

 forata)^ but are perforated like a sieve by the elongated slits 



Fi<r. 3. 







Stromatopora Hindei, Nich. : a, upper surface of a fraprnent, natural size, 

 showing the pores and oscula ; h, vertical section of a fragment, enlarged, 

 showing the obliquely arranged lamina? and interlaminar spaces; c, 

 upper surface of a fragment, enlarged. 



