RECEPTACULITES. 



127 



integuments of the wall are composed of numerous rhom- 

 boidal calcareous plates (fig. 29, B), closely fitting together, 

 and arranged in obliquely-curved intersecting rows, giving 

 fragments of the fossil very much the appearance of the 

 engine-turned case of a watch. According to Billings, the 

 points of junction of each quartette of plates in the inner 

 integument are pierced by foramina (see fig. 28), which 

 allow of a communication between the central cavity and 



Fig 29. Morphology of Receptaculites. A, Outline of a perfect, basin-shaped specimen of 

 Ilceeptaculites Neptuni, viewed in profile, of the natural size ; B, Part of the outer integument 

 of the same, enlarged two diameters, and so far weathered as to show the canals radiating 

 from the summit of the radial pillars ; c, Side view of a fragment of the same, showing the 

 radial pillars uniting the inner and outer integuments ; D, Vertical section of the same, 

 magnified, showing the outer and inner integuments (o and i), and the central canals of the 

 pillars. From the Devonian of Germany. (After Gumbel.) 



the intercolumnar spaces of the wall ; but no such apertures 

 could be detected by Gumbel in the specimens examined by 

 him ; and he thinks that this communication is effected by 

 means of minute, microscopic canals between the edges of 

 contiguous plates. The last-named observer has also shown 

 that the radial pillars of the wall are thick and nearly solid, 

 but are perforated by a central tube or canal (fig. 29, D), 



