which are readily seen after the plant has been treated with acid. The 

 colour, when growing, is bright green, and owing to the calcareous crust, 

 it frequently turns white in drying. The substance is rigid, and the plant 

 does not adhere to paper in drying. 



This is one of those lime-incrusted Algee which, on account of 

 their calcareous crust, were formerly classed among the flexible 

 Corals. The genus jPenicilhs, aptly named by Lamarck, from 

 the resemblance of its frond to a painter's brush, includes several 

 Algae of similar habit, mostly found on shallow coral-reefs within 

 the tropics. The subject of our present Plate is the only one yet 

 found in Australia ; nor am I aware of any other locality than 

 that at Rottnest Island. It is well distinguished from other 

 described species by the bead-like lower articulations, and the 

 alternating bead -like and cylindrical upper joints. 



Fig. 1. Penicillus Akbuscula; a full-grown plant, — the natural size. 2. 

 Young plants, before the formation of the stipes. 3. Portion of one of the 

 dichotomous, confervoid ramelli : — magnified. 4. Cells from the same, after 

 the lime has been removed by acid, — more highly magnified. 



