Mr. W. Lonsdale on the Genus Lithostrotion. 461 



With regard to the comprising in one genus of corals having 

 free and united corallites, the ' Archives ' contains the follov.ing 

 remark : — " Nous nous sommes assures, pour les pclypiers pre- 

 sentant la meiae organisation que le Lithostrotion striatum de 

 Fleming, que le degre de rapprochement et de soudure des indi- 

 vidus est tres-variable dans une meme espece et par consequent 

 ne saurait avoir une importance generique ^^ (p. 433). llcference 

 is then made to Lithodencbon and the other branched genera 

 above enumerated; and in support of the opinion just given, 

 Lithostr. Canadense may be quoted, though it is the only species 

 in which a bi'anched and massive composition is directly men- 

 tioned. It is however said to be " tantot en touffe subden- 

 droide, tantot moitie dendroide, moitie astreiforme, ou tout h. 

 fait massif, suivaut les divers degres de rapprochement des indi- 

 vidus " (p. 433). From this statement it appears that that coral 

 was liable to many variations of growth ; and the corallitcs in the 

 Lithodendra of Mr. Philli])s are well known to be occasionally 

 united with more or less llattened sides ; but these conditions 

 are only incidents of development. On the contrary, not one of 

 the massive or asteriform species described in the monogi'aph 

 (p. 441 to p. 445) is shown to assume a partially branched habit. 

 A variable growth marks moreover equally with an invariable 

 one, important peculiarities in the polype, and may be rightly 

 assumed as one valuable generic character. But it is not suffi- 

 cient to state that corallitcs are partially or wholly united ; the 

 nature of the junction as well as the degree of structural blending 

 should be detailed, so far as it can be ascertained ; likewise the 

 characters of lateral processes by which a connexion between 

 more or less distant branches was effected. In Lithostrotion 

 Phillipsi (Archives; the corallitcs are stated to be frequently 

 united in little series by their sides, so as to call to mind some- 

 what the arrangement oi Halysites (p. 439) or Catenipora; but 

 Count Alex, von Keyserling *, who had described the coral, and 

 refeiTcd it to Liihod. fasciculatum (Phillips), says they are united 

 by short, often proliferous transverse tubes (" verbundcn durch 

 kurze, oft proliferirende Querrohren ") ; while in Lithostr. Hur- 

 modites (p. 440. pi. 15. figs. 1, \a) and L. concameratum (p. 441) 

 connecting tubes are mentioned ; similar in the former species to 

 those of Syrinyopora ; and in L. Stokesi the union is effected by 

 expansions issuing from transverse ridges (" bouiTclets,'^ p. 440, 

 pi. 20. f. 2). All the other species noticed in the 'Archives' 

 are apparently destitute of such processes ; and the junctions 

 seem to have been accomplished either by simple contact or an 

 extension of the cellular structure, which occurs immediately 



* Reise in das Pctschora-Land, pp. 1/0-1 /I. tab. 3. fig. 2. 



