272 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 17 



ing a surface jelly 25 fx thick or more, a single outer cortical layer of 

 small, rather widely spaced, subovoid cells about 5 /x wide and to 7 /* 

 long (roundish in surface view), a subcortex of 2-3 layers of larger 

 arachnoid cells, and a medulla of rather sparse, anticlinal filaments of 

 2-4 linear cells extending across from subcortex to subcortex; highly 

 refractive medullary filaments apparently absent; carpogonial branches 

 2-celled, borne in ampullar systems separate from and smaller than those 

 bearing the prominent auxiliary cells; developing cystocarps scattered, 

 about 150 /A in diameter, completely embedded; carpospores in a com- 

 pact, rounded, pedicellate mass, angular, 10-12 /a in greatest diameter; 

 antheridia and tetrasporangia unknown. 



Type: Holotype is Dawson 433-40, Feb. 5, 1940, on sheet 28, 

 including slides 2209-2211, 2218, in HAHF. 



Type locality: On a rocky bottom at a depth of 110-116 m., 2 

 miles north of Isla Partida, Gulf of California, Mexico. 



Halymenia abyssicola is similar in several respects to some of the 

 variants of H. actinophysa, but it appears to be distinct in the several 

 features indicated below. The cortical cells are ovoid, mostly rounded 

 as viewed from the surface, and 5 /a or less in greatest diameter. In H. 

 actinophysa the surface cells are ± angular and mostly 7 fi or more in 

 greatest diameter. H. abyssicola has a thick surface jelly which has not 

 been observed in H. actinophysa. The jelly is not conspicuous, however, 

 and must be viewed quickly with the aid of stain, for it dissolves in a 

 rather short time after dry material has been soaked up. The highly 

 refractive medullary filaments commonly present in H. actinophysa are 

 absent in the type of H. abyssicola. The subcortical cells are prominently 

 arachnoid and relatively more compactly layered than in H. actinophysa. 



Halymenia megaspora sp. nov. 

 PI. 3, figs. 26-28 ; pi. 14, fig. 58 



Thallis membranaceis, irregulariter orbicularibus vel reniformibus, 

 plerumque latioribus quam altioribus, 10-15 cm. altis, 200-400 fi crassis, 

 paene sessilibus ; marginibus integris at sinuatis, plus minusve lobatis vel 

 laceratis; cortice exteriori e filamentis anticlinalibus ramosis e circiter 

 tribus cellulis exiguis compositis; carposporis in massa laxa dilapsibili 

 contentis, magnis, 20-30 fx diametro, baud valde angularibus. 



Thalli membranous, gelatinous, dull rose in color, irregularly orbicu- 

 lar to reniform, usually broader than tall, to 10-15 cm. tall, 200-400 fi 

 thick, almost sessile, attached by a small fleshy peg and disc; margins 

 entire but sinuate, ± lobed or lacerate; transection showing a fairly 



