No. 3] REMARKS ON NORTHERN LITHOTHAMNIA. 7 



destruction an opening may be formed in the central parts of an 

 inverted plate-shaped specimen, i. e. in the second half of the 

 original one, and the specimen becomes more or less wreathlike. 

 Cp. Norw. Lithoth. pi. 12, fig. 2, pi. 13, fig 3. 



It seems probable that also bigger marine animals than those 

 presumed above may contribute to the rise af greatly varying or 

 reduced forms, particularly of rather densely branching Lithothamnia. 

 Thus crabs or other bigger Crustacea will cut off branches or 

 systems of branches from the alga, in order to obtain coveted 

 food among the smaller animals living in or between the branches 

 of the alga. The branches cut off in this way no doubt often 

 grow on, as is the case with branches broken off by the waves x ) 

 or by the use of different kinds of fishing tackle. 2 ) The form 

 soluta of Lithothamnion fruticulosum mentioned 1. c. may perhaps 

 have risen in such a way. Cp. 1. c. p. 7, fig. 18—33. 



Another enemy to Lithothamnia is the family of the boring 

 algae. Their destructive work sometimes matches with attacks of 

 animals. Of the boring algae 'occurring in the boreal-arctic areas 

 particularly Ostreobium Queketti Born, et Flah. is found in Litho- 

 thamnia, chiefly in older specimens of such ones. It otten occurs 

 so numerously as to form something like a dense network in large 

 parts of the host plant. 



The calcareous algae have also a third enemy, a purely me- 

 chanical one, friction. It exercises a destructive influence particularly 

 on older specimens, when the alga, as mentioned above, is growing 

 in places with strong currents, i. e. in narrow and shallow sounds 

 or in places in a fjord where the tidals run very strongly. In this 

 case the friction of the water effects that the upwards turning 

 part or even the greater part of the knolls lying freely on the 

 bottom gets specked with the friction or is partly torn away. 

 Cp. Norw. Lithoth. pi. 4, fig. 1—2, pi. 6, fig. 2—3, pi. 10, fig. 5, 



1 ) M. F o s 1 i e. A Visit to Roundstone in April. — Irish Naturalist. Vol. VIII. 

 Dublin 1899. Pag. 175. 



2 ) M. F o s 1 i e. Die Lithoth amnien des Adriatlschen Meeres und Marokkos. 

 Wissensch. Meeresuntersuchungen. Neue Folge. VII. Band. Abt. Helgoland. 

 H. 1. Oldenburg i. Gr. 1904. Pag. 10. 



