true Carboniferous NummuUte. 227 



at the periphery. When the surface of the test is not worn, the 

 radiation is either very indistinct or appears in the form of 

 curved lines of somewhat darker colour, but without sensible 

 limbation ; but in Aveathered specimens not only are the lines 

 more or less elevated, but the centre from which they proceed 

 is thickened and the test becomes to some extent umbonate also. 



An accidentally split specimen (PL XII. fig. 4) will serve the 

 purpose of a horizontal section. It consists of three convolu- 

 tions, the outermost having sixteen chambers, and the second 

 twelve or thirteen. Another, somewhat larger individual has 

 precisely similar septation ; so that, without assigning any great 

 importance to it, the drawing may be assumed to represent a 

 specimen with about the normal number of chambers for the 

 adult condition. 



The primordial chamber has been measured in three ex- 

 amples, and the diameter found to be "004, '003, and '0027 of 

 an inch, being respectively from -f to ^ of the entire diameter 

 of the test. 



The minute tubulation of the shell is perfectly preserved, 

 and may be easily seen in the transverse section under a 

 magnifying-power of 100 diameters, as in PI. XII. fig. 3. 



The canal-system of the septa and marginal cord may be 

 traced here and there, though only imperfectly. The trans- 

 verse section (fig. 3) gives distinct evidence of the existence 

 of the marginal cord ; but the details of the structure are 

 obliterated ; and in the more highly magnified drawing (fig. 5) 

 indications are not wanting of canals traversing the sejita as 

 well as the su])plementary skeleton. 



Such is a detailed account, as far as can be furnished from 

 the materials available, of the finer specimens of this Carbo- 

 niferous Nummulite; and in the absence of larger individuals 

 or of fragments indicating their existence, they may fairly be 

 supposed to be adults and fully developed examples of the 

 species. But, in addition to these, a number of smaller indi- 

 viduals have been found apparently belonging to the same 

 form, though neither so uniform in external appearance nor 

 so unmistakably nummuline in character. One or two are 

 somewhat cxplanate in their mode of growth, and if mature 

 may pertain to an "Assiline" variety. Others, smaller still, not 

 much more than a hundi-edth of an inch in diameter, are 

 unsymmetrical, the convexity of the two faces being unequal 

 and irregular. They probably represent either one of the 

 early stages of the organism or perhaps an arrested condition 

 of growth. Their precise relation to the fully dcvclo])e(l form 

 must be left for future determination, in the lack of sufficient 

 specimens to work the question fully out. 



