462 Mr. W. Lonsdale on the Genus LIthostrotion. 



within the wall of the corallite. Sometimes contiguous branches 

 in the Lithodendra of Mr. Phillips are not united_, and can be 

 separated wiihout a fractured surface; but where a junction had 

 taken place, the coalesced walls could not, in general, be severed 

 without producing a scar on one or both of the stems. The 

 corallites of L. Canadense, which had become prismatic by con- 

 tact (" par rapprochement ") are also stated to be often detachable 

 by the hammer without breaking (p. 434). Mr. Phillips's fig. 14 

 (Geol. Yorks. pi. 2) of Lii iiodendron irregular e exhibits two in- 

 stances of slightly distant branches being united by lateral deve- 

 lopments; and polished transverse sections of apparently the 

 same species gave many examples of the mode in which junc- 

 tions had been formed among corallites very near each other, as 

 well as in close contact. The latter showed along the line of 

 junction a strong boundary-wall more or less flattened, and 

 sometimes the adjacent cellular structure was slightly irregular. 

 Where a small interval had existed, an outer extension of one of 

 the coi'aUites effected the union ; and this elongation was wholly 

 cellular, or similar to the portion of the stem from which it 

 issued. The cells were as regularly formed and arranged as 

 within the corallite ; and there was no indication of a point, 

 which might have become an axis, or the centre of an abdominal 

 cavity. Moreover, no line of separation or partition-wall oc- 

 curred between the extension and the body of the corallite ; care 

 being taken to guard against an inner circle of dissepiments ; 

 but at the junction with the other stem was a distinct wall, si- 

 milar to that just noticed as existing in united contiguous sur- 

 faces. These lateral elongations were not regarded as incipient 

 corallites, which had been impeded in their growth, for reasons 

 given in the remarks on those productions. So far as observed, 

 they, however, invariably issued from only one of the united 

 branches, as if their development had depended upon some pe- 

 culiar requirement in the polype : M. Milne-Edwards and M. J. 

 Haime nevertheless state, that in Lithostr. [Lithodendron) irre- 

 gulars the corallites, especially in the lower part, "portant des 

 bourgeons dont beaucoup ont avorte et semblent s'etre soudes 

 aux polypierites voisins" (Arch. p. 437). The nature of the 

 processes above mentioned, and the conditions under which they 

 were developed, as well as the extent to which their characters 

 may have been influenced by direct contact in corallites, remain 

 to be investigated and described. It is enough for the present 

 inquiry to know, that they exist in certain species ; and that in 

 others, contiguous branches are often laterally united, and can- 

 not under such circumstances be separated without fracture. 



It is impossible from want of information to determine whether 

 Lhwyd's fossil was separable with entire exteriors ; and as Park- 



