466 Mr. W. Lonsdale on the Genus Lithostrotion. 



Stf/l. inconferta^, that the reader may form his own opinion re- 

 specting it, and be able to compare the statement with the cha- 

 racters assigned to young branches in Lithod. irregulnre and L. 

 sexdecimale. " The additional columns were produced by a sub- 

 division parallel to one of the facets of the pre-existing column, 

 and not by the development of a circular germ. Externally the 

 partition was rendered visible by a line commencing in outer 

 walls on opposite sides of a column, and ranging upwards, it 

 almost immediately marked a clear boundary between two distinct 

 columns." * * * * " In a section purposely made about half a 

 line below the point where a subdivision was visible, the trans- 

 verse under surface exhibited not the least sign of any irregularity 

 in the lamellae or in the interstitial plates. The young or offset 

 column, which commenced immediately above the section 

 (fig. 2 b), nearly subdivided the facets from which it sprung ; but 

 its area was much less than half that of the pre-existing column.'* 

 * * * * " The structure exhibited in this uneven plane " (the 

 obliquely fractured, upper sin-face of the young corallite, fig. 2 h, 

 pi. A. op. cit.) " was much less regular than that in the section 

 beneath, though not very different from the arrangement of the 

 component laniinse near the sides of other columns in which no 

 subdivisions existed : traces also of extensions upwards of the 

 lamellae of the undivided column were likewise detectable, in- 

 dicating that the polype of the young column possessed, to a 

 certain extent at least, the secreting membranes of the old.'' 



From the foregoing statements respecting what had been ob- 

 served in the reproductive processes of Lithodendron and Stijlas- 

 trea, it is inferred, that additions were somewhat similarly effected 

 in each case, or by an extension into the offspring of certain por- 

 tions of the parent structures — that the operation was a modifi- 

 cation of fissiparous productions — and that it should be carefully 

 distinguished from purely gemmiferous developments. 



The mode of increase in the Columnaria of Mr. Dana is not 

 given in the description of the genus f. In Nemaphyllum, small 

 circular buds were produced within the area of the parent star; 

 and Prof. McCoy's delineation exhibits the characters of a true 

 germ. A marked difference therefore exists between the manner 

 of eflfecting additions in that genus, and in Lithodendron or in 

 Stylastrea. 



As respects the internal composition of the fossils under con- 

 sideration, the characters assigned in the ' Archives ' to Lithostro- 

 tion, and before quoted, express very nearly the construction of 

 the Lithodendra of Mr. Phillips, omitting the words " tantot 



* Geol. Riissiii, Appendix A. p. G20, commencing line 11, pi. A. fig. 2, 

 2 0-2 c. 



t Exploring Expedition, Zoopliytes, p. 362-;S6.3, 1846. 



