472 Mr. W. Lonsdale on the Genus Lithostrotion. 



in longitudinal sections of the coral, believed to be Lithod. fasci- 

 culatum, some of the intervals between the inclined laminae of 

 the inner area were not wholly traversed by lamella?, but pre- 

 sented a structure somewhat analogous to that given in the ac- 

 companying diagram. In the other species before 

 mentioned no longitudinal sections were examined. 

 Another particular in the lamellae of Lithodendra, 

 requiring investigation, is the composition. Ac- 

 cording to the specimens of L. fasciculatum and L. 

 irregulare which were examined, the opake, white sub- 

 stance of the lamellae was traversed along the middle, in trans- 

 verse sections, by a fine translucent line, resembling in colour the 

 calcareous spar which filled the cells and other lacunae of the 

 corallites. It was easily detected in the fossils considered identical 

 with Lithod. fasciculatum and L. irregulare, occurring in the nar- 

 row plates a3 well as in the broad ; but it was not discovered in 

 L. sexdecimale. No lamellae vertically divided, as in Stylastrea, 

 were observed in a rough, partially fractured specimen of L. ir- 

 regulare, though in polished, longitudinal sections of L. fascicu- 

 latum a translucent line often ranged down the middle of the 

 vertical plates. The massive or basaltiform corals which were 

 examined had in the inner area straight-edged lamellae ; and in 

 Mr. Dana's Columnaria, Parkinson's Lithostrotion, Cyathophyllum 

 basaltiforme and Nemaphyllum the structure is probably similar. 

 How far any of the latter corals have lamellae composed of two 

 separable laminae remains to be ascertained. 



These defective observations afford no data for satisfactory 

 comparison, as they do not rest on clear structural evidence. It 

 is however probable that the membranes from which the lamellae 

 were produced had a periodical extension in one case, but not in 

 the other ; and in certain instances, as respects both branched 

 and massive species, the lamellae were apparently biplated. 



A survey of the characters noticed in the preceding para- 

 graphs of this article will afford the following conclusions re- 

 garding the fossils which have been the subjects of consideration : 

 1st, the habit of growth, mode of union, and external condition 

 of parted stems are dissimilar in Lithodendra (Phill.) and the 

 basaltiform corals which were examined— omitting Nemaphyllum 

 from the summary, as it is believed not to be truly columnar, and 

 to be otherwise essentially different from the Zoantharia with 

 which it is associated in the ' Archives ' ; 2ndly, additional coral- 

 lites seem to have been produced in branched as well as massive 

 species by equivalent processes, or by modified fissiparous opera- 

 tions, and not by simple germs ; 3rdly, the internal structures 

 vary in the number of the component parts to the extent to 

 which they could be ascertained ; and in the characters of each 



