302 Mr. J, Thomson and Dr. H. A. Nicholson on the 



The septa are present in a well-developed form in the 

 exterior portion of the tabulate area, but do not exist at all 

 in the outer vesicular zone, or only extend into the latter 

 region in a very rudimentary and imperfect form {PI. XVI. 

 figs. 1-3). Secondary septa are usually, if not always, pre- 

 sent ; and the primary septa for the most part stop short at 

 a little distance from the columella. In some cases, however, 

 a few of the primaiy septa seem to be continued inwards as 

 far as the columella. When viewed in transverse sections 

 (PI. XVI. figs. 1a, 2 a, & 3 a), the septa are seen to be 

 united by delicate transverse dissepiments, which, however, 

 are not developed between the septa in their inward extension, 

 and become sparse and irregular as the septa are traced out- 

 wards to the outskirts of the vesicular zone. 



The genus Lonsdaleia was first clearly defined by Prof. 

 M'Coy [he. cit.) ; but he included only the fasciculate forms 

 under this name, and erroneously referred the astrteiform 

 species to Strombodes. The essential structural characters of 

 the genus, however, had at an earlier date been fully recognized 

 by Mr. Lonsdale (Murch. Vern. & Keys. Russ. & Ur. p. 602) ; 

 but he considered that the name of Lithostrotion was the one 

 properly applicable to these corals. Milne-Edwards and 

 Haime (Brit. Foss. Cor. p. 190) first showed that the name 

 of Lithostrotion should properly be applied to the group of 

 corals of which L. hasaJtiforme is the type ; and in this they 

 have been supported by most subsequent writers on the subject. 

 Fromentel, however, took the retrograde step of separating the 

 astrgeiform species under the name of Stylidophyllum (Poly- 

 piers Foss. p. 316) ; and Dybowski has so far adopted the 

 same course as to restrict the name of Lonsdaleia solely to the 

 same species (Mon. der Zoanth. scler. rug. p. 83). 



The zoological characters of tlie genus Lonsdaleia are so 

 well marked that there is little chance of its being confounded 

 with any other. From the true Strombodes^ Schweig., from 

 Spongojjhyllumj E. & H., and from Endophyllum, E. & H., it 

 is at once distinguished, amongst other characters, by its pos- 

 session of a columella. From Lithostrotion and Diphyphyllum 

 it is separated by the fact that the septa are not in direct con- 

 nexion Avith the outer wall ; whilst the latter genus has no colu- 

 mella, and this organ in the former genus appears as a compact 

 styliform rod. By far the nearest allies of Lonsdaleia^ as at 

 present understood, are Chonaxis^ E. & H., and Axojphyllum^ 

 E. & H. The former of these appears to difi'er from Lonsdaleia 

 solely, or chiefly, in the fact that the external walls are want- 

 ing, and the corallites are united together directly by the amal- 

 gamation of their vesicular zones. The genus Axophyllum^ 



