172 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 12 



LITHOTHAMNIUM Philippi, 1837 



Plants crustose, or erect and often branching from a crustose base; 

 structurally of two layers, the basal or hypothallus spreading, the upper 

 or perithallus transversely zonate ; sporangial conceptacles soriform, super- 

 ficial or somewhat immersed, at first separate but later those adjacent 

 fusing, discharging through several pores ; cystocarpic conceptacles super- 

 ficial or slightly immersed, conical or subconical, at first with a projecting 

 tip, discharging by an apical pore. 



KEY TO SPECIES 



1. Plants crustose, smooth or with warty prominences but without 

 slender erect branches 2 



1. Plants with erect branches clearly much longer than broad . 3 



2. Plants firmly adherent to the substratum (often loosened by bor- 

 ing animals), with wartlike or irregular short simple excrescences 

 0.5-2.0 mm diam. ; perithallus of subquadrate cells 6-9 /x diam., 

 or cells vertically elongated to 7-14 /x; sporangial conceptacles at 

 first convex, later flattened and hardly prominent, 300-500 [i 

 diam L. pacificum 



2. Plants with a well-developed crust, bearing short simple approxi- 

 mate or coalescing projections 3.5-5.0 mm thick; perithallic cells 

 7-14 IX tall, 7-9 fi broad ; medullary cells 14-20 fx. tall, 7-9 /a diam. ; 

 sporangial conceptacles convex, flattened or depressed in the 

 central part, 400-800 fi diam L. validum 



3. Plants enclosing hard objects, or sometimes free, branching rela- 

 tively sparse but irregularly repeated, sometimes short and con- 

 gested, often warty, 1-3 mm diam. ; medullary cells 14-29 fi long, 

 9-14 /J. diam.; sporangial conceptacles convex or flattened, little 

 prominent, 300-650 /x diam. ; cystocarpic conceptacles 400-700 fi 

 diam L. indicum 



3. Plants free, irregular or subglobose, 0.5-2.5 cm diam. ; sparingly 

 repeatedly subdichotomously to irregularly branched, the branches 

 approximate or a little remote, frequently a little tapered, 0.75- 

 2.0 mm diam.; medullary cells 14-36 /x long, 7-14 /x diam.; spo- 

 rangial conceptacles convex or flattish, moderately prominent, 

 300-650 IX diam L. australe 



