79 



in its development fully accords with L. fornicatum. It at first 

 fastens itself to, encompasses or nearly encompasses shells, stones 

 or other hard objects, being closely and firmly attached to its 

 substratum. Pl. 14, fig. 2. It forms a thin crust, or now and 

 then smaller lobes, from which issue short and simple, or once or 

 twice divided branches, with very short axes, muen anastomosing 

 in their lower part. Sometimes the crust increases in thickness, 

 though never much, but apparently more frequently getting thinner 

 or disappearing, which not unlikely is caused by attack of animals. 

 The plant by and by gets hollow, loosens itself from the substratum 

 (pl. 14, fig. 3) and at length assumes a more or less depressed 

 cup-shaped form, attaining a diameter of up to 25 cm. Pl. 14, 

 fig. 1. The inner or lower side of such specimens partly becomes 

 somewhat rubbed, so that the interwalls here and there are visible 

 from this side, partly and probably more commonly is still provi- 

 ded with a thin crust, or a new and in part local crust-like for- 

 mation developed from this side. In the part turning upwards the 

 branches always are short and much anastomosing, especially in 

 younger specimens often looking like simple and short processes 

 issuing from an apparently rather thick crust-like hypothallus, ho- 

 wever, in the main composed of anastomosed branches or pro- 

 cesses. The edges of opened specimens sometimes bend and grow 

 inwards, and together with branches afterwards developed from 

 the inner or lower side of the plant by and by appear to replenish 

 at least a part of the cavity or concave base. The branches or 

 processes are terete and cylindrical, seldom slightly attenuating to- 

 wards the tip, straight and fastigiate, in general 1 — 1.5 mm. thick, 

 with obtuse or thickened obtuse ends. 



A solitary and sterile specimen, in habit as well as in structure 

 fully agreeing with the named form, seems to have developed itself 

 freely on the bottom. It is nearly hemispherical, the longest dia- 

 meter about 15, the shortest about 9 cm., but the central portions 

 fully destroyed and filled by numerous boring-muscles leaving a 

 peripherical portion about 1 — 1.5 cm. in thickness. The branches 

 of this portion are much anastomosing. Thus it appears, as if 



