Dr. H. A. Nicholson on the Genus Stromatopora. 11 



ccntrically •wrinkled calcareous membrane, precisely similar to 

 the epitheca of a Favosites or Fistulipora. Usually the species 

 forms extensive crusts of no great thickness ; but I have one 

 specimen in wliich the organism is attached by a broad base 

 to a large IleliopliyUum^ from which it spreads out laterally in 

 all directions as a horizontal expansion, the under sm-face 

 being covered with a wrinkled " epitheca," and having been 

 obviously free. 



3. Stromatopora perforata^ Nicholson. 

 Spec. char. Fossil composed of cmsts of varying thickness, 

 made up of thin concentrically arranged calcareous lamina?, 

 the interspaces between which are rendered vesicular by ver- 

 tically disposed calcareous rods or dissepiments. From four 

 to five lamuiie with their intervening interspaces occupy the 

 space of one line. Upper sm-face undulating, and covered 

 Avith very numerous rounded apertures, which vary in widtli 

 from two thirds of a line to one line, and are situated at dis- 

 tances apart of a line, more or less. These apertures are 

 usually placed at the summit or on one side of conical emi- 

 nences ; or they are elevated above the general surface, the mar- 

 gin of the opening on one side being in general higher than 

 on the other. These apertures are the orifices of vertical or 

 somewhat oblique canals, which penetrate the vesicular tissue 

 of the fossil, and arc lined with a delicate calcareous mem- 

 brane, marked with faint encircling stria;. For a certain dis- 

 tance (two or three lines) each canal descends in a straight 

 line, and then is ciu'ved so as to become nearly parallel to the 

 lower surface of the mass, at the same time contracting in its 

 diameter (fig. 2, c). Between the oscula, as just described, 

 the surface is covered with a fine miliary granulation, com- 

 posed of minute pustules placed close together and arranged 

 in in'egular vermicular or sinuous lines. 



Stromatopora perforata is perhaps the most remarkable 

 species of the genus which has been yet described ; and it can- 

 not be doubted that it is a genuine member of the Calcispongia>, 

 though in some respects an abnormal one. In its internal 

 structure it agrees altogether with S, tuherculata, S.(/ranuIata, 

 and ^S'. mammillata ; and with the two former of these it agrees 

 further in the possession of a series of a])erturcs which cannot 

 be any thing but " oscula." No " pores," however, have been 

 detected, unless some of the surface-tubercles should in reality 

 be perforated, which is likely enough. 



S. perforata is readily distinguished from S. tuherculata by 

 the much greater number and closer arrangement of the oscula, 

 by the elevation of these apertures above the general surface, 



