226 DE. G. J. HINDE ON SEPTASTE^A, d'oEBIGNT (1849), 



the insertion of the mesenterial muscles are shown in some 

 specimens. 



6. The septa in Septastrcea consist of a central layer, which in 

 microscopic sections is dark and enclosed on both sides by lighter 

 layers of calcareous tissue. The dark central layer is divided in the 

 median plane, so that each lamina of the septum consists of a 

 primary dark inner layer and an outer lighter layer of stereoplasm. 

 The inner dark layer consists of transverse growth-lines and delicate 

 longitudinal ridges and grooves of a powdery, incoherent material ; 

 its present character is probably due to change in fossilization. 

 The enclosing lighter layer of stereoplasm, on the other hand, is 

 compact, fibrous, subcrystalline, and of an ivory-white appearance. 

 The thecal wall is merely an extension of the septal laminae, and 

 has a similar minute structure. 



7. The structure of the theca and septa in Sejjtastrcea corresponds 

 closely to that of the recent and fossil genus Flahellum. 



8. Only two species are included in Sejptastrcea, as now defined, 

 viz., S. Forhesi, E. & H., and S. (Columnaria'l) sexradiata^ 

 Lonsdale, sp. 



EXPLANATION OF PLATE IX. 



Fig. 1. Upper portion of the type specimen of Septastrcea Forhesi, E. & H. 

 (now in the Brit. Mus. Nat. Hist.), showing the disposition of the 

 corallites and the interstitial buds (b) at the growing ends of the 

 branches. Nat. size. 



2. Corallites from the surface of a specimen of >S', Forhesi, showing the 



early stage of growth of a young individual {b), in which mere 

 traces of septa appear in a shallow, triangular depression between 

 full-grown calices. Enlarged five diameters. Specimen in Brit. 

 Mus. 



3. 3 a, 3 h. Three calices of 8. Forhesi, showing variations in the septal 



development. Enlarged three diameters. 



4. Four corallites from the interior of a specimen of S. Forhesi, showing 



great variation in the disposition of the septa. Enlarged three 

 diameters. 



5. A transverse section of a corallite from the interior of a specimen of 



8. Forhesi, showing curved and intertwisted septa. Enlarged five 

 diameters. 



6. Calices from the type of Septastrcea sexradiata, Lonsd., sn. (now in 



the Museum of EJing's College, London), showing the development 

 of the third cycle of septa. Eulai'ged five diameters. 



7. A corallite from the interior of S. Forhesi, showing the bilaminated 



character of the septa, and their mode of union with each other. 

 Enlarged eight diameters. 



8. A portion of the interior of a coralhte of S. Forhesi, showing the 



divergence of the septal laminae to form the wall or theca, and the 

 extension of the dark primary laj-er or centre of calcification in the 

 median line of the septa, to the exterior of the wall. Enlarged 

 twenty diameters. 



9. A portion of a septum of 8. Forhesi, which has split along its median 



plane, and shows the smooth inner face of the septal lamina with 

 the transverse growth lines, and traces of the longitudinal ridges. 

 Enlarged fifteen diameters. 



10. A portion of the inner layer of a septal lamina of 8. Forhesi, showing 



the longitudinal ridges and grooves immediately beneath the trans- 

 verse growth-lines. Enlarged forty diameters. 



