184 Dr. H. A. Nicholson and Mr. R. Etheridge^ Jun., on 



region of the coralium, exhibit exceedingly characteristic 

 appearances. In tangential sections (PI. IV. tig. 4, and wood- 

 cut, fig. 2, A) the corallites are seen to be polygonal or sub- 

 polygonal in shape, and to be furnished with tliin, completely 

 amalgamated walls. The thickness of the walls varies 

 according as the plane of the section corresponds with the 

 thickened nodes of the walls or traverses the unthickened 

 internodes (PI. IV. fig. 4). At all the angles of junction of 

 the corallites are placed well-marked acanthopores, which are 

 sometimes minute, but at other times large, circular, thick- 

 walled, and showing a distinct lumen (woodcut, fig. 2, A). 

 In longitudinal sections (PI. IV. fig. 5, and woodcut, fig. 2, 

 B) the walls of the corallites are seen to be thin, but to be 

 rendered moniliform by small fusiform thickenings which are 

 placed at corresponding levels in all the tubes. Tabular are 

 developed from these nodal points, but vary much in their 

 numbers. Sometimes there are only very few of these struc- 

 tures, but at other times they may be developed from almost 

 every successive pair of nodal points. 



Thin sections of the type-specimen of S. crlnita show phe- 

 nomena which are at first sight strikingly unlike those exhi- 

 bited by the specimens just alluded to. Thus in transverse 

 sections of the type-specimen (PI. IV. figs. 1 and 2) the 

 corallites are seen to be polygonal and for the most part fur- 

 nished with thin dark linear walls, at the angles of junction 

 of which are placed small acanthopores. Here and there, 

 however, at tolerably regular intervals, we observe groups of 

 comparatively small-sized corallites, with thicker walls and 

 larger acanthopores (PL IV. fig. 1). The peculiar feature of 

 this specimen, however, lies in the fact that the thin proper 

 walls of the corallites are uniformly lined by a continuous 

 investment of brown calcareous substance of considerable 

 thickness (PI. IV. fig. 2). This investment is so invariably 

 present, is so constant in its thickness, and so exceedingly 

 regular in its development, that it has every appearance 

 presented by the layer of secondary sclerenchyma which is 

 deposited on the inside of the proper wall in Pachypora^ 

 Laceripora^ and other similar corals. Precisely the same 

 thing is exhibited by longitudinal sections of the type-specimen 

 (PI. IV. fig. 3), which show the proper moniliform walls of 

 the corallites invested on both sides by the same dense and 

 regular deposit. Our first impression therefore was that we 

 had to deal here with a thick secondary investment of scleren- 

 chyma, such as is found lining the visceral chambers in various 

 types of tabulate corals. Further investigation, however, 

 satisfied us that this view was untenable, and that this curious 



