CLATHRODICTYON STRIATELLUM. 157 



nounced in some specimens than in others, but are always gentle and regularly 

 curved. The lamina? are also regularly crumpled in the same manner as in G. 

 vesiculosum, but less completely, so that there is no appearance in vertical sections 

 of rows of lenticular vesicles, such as are so cluaracteristic of the latter species. 

 Each infolding of the lamina is, however, prolonged downwards 1 into the inter- 

 laminar space below in the form of a more or less complete radial pillar. Some of 

 the radial pillars are quite short, others project about half-way into the inter- 

 laminar space ; others cross the space and become connected with the lamina 

 below ; finally, a few spring from the upper sides of the lamina?. A further very 

 characteristic point about the radial pillars is that they are very commonly double 

 at their bases, where they spring from their producing lamina. 



Tangential sections (Plate XIX, fig. 9) of this species are much more charac- 

 teristic than is usual in the genus Clathrodictyon. Where such a section traverses 

 an interlaminar space, the cut ends of the radial pillars are seen in the form of dark 

 granular masses, of considerable size, and usually of a more or less elongated or oval 

 shape. Where the section more or less closely coincides with a concentric lamina, 

 the cut ends of the radial pillars are more closely set and larger in size, and often 

 form a sort of mosaic pavement, or at other times a loose reticulation. Tangential 

 sections are also unlike similar sections of most species of this genus in the appa- 

 rent absence of astrorhizal canals. 



Obs. — In its general features Clathrodictyon striatellum can hardly be confounded 

 with any other member of the genus. In external and superficial characters it 

 makes a close approach to G. regulare, Rosen but its size is usually much greater, 

 its general texture is coarser, and its internal structure is quite different. Its most 

 distinctive characters are the gentle and regular undulation of the concentric 

 lamina?, and the peculiar form of the radial pillars which spring, very commonly 

 by a double base, from the under sides of the lamina?, and often fall short of the 

 upper surface of the lamina next below. The exposed surfaces of the concentric 

 lamina? in well-preserved examples show, much more clearly than is usual in the 

 genus, the presence of innumerable zooidal pores. The radial pillars produce no 

 connecting-processes or "arms;" whereas these structures are occasionally deve- 

 loped in G. regulare. Lastly, the present form shows a more complete absence of 

 the astrorhizal system — so far as my observation goes — than is the case in any 

 related form of Clathrodictyon. 



My identification of this form as the one which D'Orbigny had in view in esta- 

 blishing his Stromatopora strlatella is based upon an examination of Lonsdale's 

 original specimen, which served as the type of the species to the French pala?onto- 



1 In the illustrations which I formerly gave of vertical sections of this species (PI. I, fig. ], and 

 PI. V, fig. 3), the figures were inadvertently reversed in position, so that the radial pillars are repre- 

 sented as growing from the tipper sides of the laminae, instead of from the lower as is really the case. 



