7 



1. c, that in thin crusts of Lithothamnion tenue Rosen v. (L. 

 Stromfeltii mini) the structure may rather approach that of Litho- 

 phyllum Lenormandi (Ares ch.). I found in the former the struc- 

 ture occasionally so nearly approaching, or even almost fully coin- 

 ciding with that of the last named species, that in my opinion any 

 true limit cannot be drawn. Other and coarser species of both 

 genera seem to approach one another much in habit, and probably 

 they are also as to the structure nearly related. Lithoph. crispa- 

 tum Hauck, Meeresalg. p. 270, t. II, fig. 3 reminds one much 

 of certain forms of Lithoth. incrustans f. Harveyi (L. polymorphum 

 Harv.), and Mr. Batters informs me, that the latter often comes 

 near to Lithoph. expansum (Phil.) in appearance. On the other 

 hand Lithoth. dendatum (Kutz.) Aresch. seems as well to be 

 referrible to Lithophyllum as coarser forms of Lithoph. cristatum 

 (Menegh.), supposing the structure of these species stands in the 

 same relation as Lithoph. decussatum and Lithoph. expansum to 

 other species of Lithothamnion. Cp. Hauck 1. c. t. II, fig. 2, 5 

 and Solms-Laubach 1. c. L. investiens occasionally reminds 

 one of certain forms of Lithoph. lichenoides in habit, and even as 

 to the structure much approaching, or perhaps nearly coinciding 

 with that of the named species. I, however, have not had the 

 opportunity to examine any of the coarser forms of Lithophyllum. 

 The structure is in all rather varying, and also the size of the 

 cells may be somewhat differing in specimens of one and the same 

 species. 



I, therefore, consider Lithophyllum a not wel.1 characterized 

 subgenus of Lithothamnion. I have, on the contrary, been in 

 doubt whether it ought not, perhaps, to be drawn in even as such. 

 Farlow 1 ) subsumes it under Melobesia, and Batters 2 ) considers 



hierher audi die meisten Lithophyllen zu rechnen sein. Rei L. decussatum 

 und L. expansum tritt ein derartiges Dickenwachsthum, wennschon in rudi- 

 mentarer Form, gewohnlich auf; dasselbe kann soweit gehen, dass die 

 ersterzeugten Conceptacula ins Gewebe versenkt, und dass iiber ihnen neue 

 gebildet -\verden. Zwei dergleichen ubereinander gelegene Schichten fanden 

 sich ofters, drei erinnere ich mich bei L. decussatum nur selten gesehen 

 zu haben*. 



!) Mar. Alg. New Engl. p. 179. 



2) Mar. Alg. Berw. p. 139. 



