CLATIIRODICTYON REGULARE. 155 



astrorhizae. Lastly, though the fragmentary nature of my material precludes 

 my forming a clear notion as to the mode of growth of the species, the coenosteum 

 may be stated with certainty to be massive and not laminar. 



Distribution. — The only known example of this form was collected by Mr. 

 Champernowne in the Middle Devonian Limestones of Pit Park Quarry, Dartington, 

 South Devon. 



14. Clathrodictton eegulare, Rosen sp. PI. XVIII, figs. 8 — 11a. 



Stbomatopoea eegulaeis, von Rosen. TTeber die Natur der Stromatoporen, p. 71, 



pi. ix, figs. 1—4, 1887. 



Clatheodictton eegulabe, Nicholson. Ann. Nat. Hist., ser. 5, vol. xix, p. 10, 



pi. ii, figs. 5 and 6, 1887. 



The coenosteum in this species is of small size ; sometimes laminar and discoidal, 

 with a basal epitheca, sometimes encrusting foreign bodies. The largest specimen 

 examined is less than 5 cm. in diameter, with a maximum thickness of little more 

 than a centimetre. As the concentric laminae are nearly horizontal, or only slightly 

 undulated, the surface is smooth, and " mamelons " are absent. The surface, 

 however, often exhibits the edges of the exfoliated laminae (Plate XVIII, fig. 8) ; 

 and in well-preserved examples (fig. 9) it is seen to be studded with small rounded 

 tubercles representing the free ends of the radial pillars, which often send out 

 radiating horizontal prolongations, enclosing minute interstitial pores. 



As regards internal structure, the skeleton is made up of horizontal or slightly 

 flexuous concentric laminae, of which about six (or five interlaminar spaces) occupy 

 the space of 1 mm. The laminae (Plate XVIII, figs. 10 and 10 a) are 

 thick, often traversed horizontally by a median dark line and slightly crumpled. 

 At each point of inflection the lamina sends down from its under surface a stout 

 radial pillar, which may only project a short way downwards into the interlaminar 

 space, but more commonly becomes connected with the lamina next below. The 

 interlaminar spaces thus become broken up into rows of regular oblong cells, 

 which are upon the whole slightly convex on their superior aspect, and which, 

 though very variable in this respect, are mostly about one-third of a millimetre in 

 length. Tangential sections (Plate XVIII, figs. 11, 11 a) exhibit large dark 

 rounded dots, representing the cut ends of the radial pillars. These are often 

 connected together by distinct radiating " arms," thus showing an imperfect form 

 of the " hexactinellid " structure so characteristic of the species of the genus 

 Actinostroma. Astrorhizae do not appear to be developed at all. 



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