22 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 17 



Type: Holotype is Gardner 5023, on sheet 294550 in the Herbar- 

 ium of the University of California, Berkeley. 



Type locality: In Sertularia furcata. La Jolla, Calif. 



Mexican distribution: Pacific Baja Calif. — D. 9660, in Sertu- 

 laria furcata in drift, Bahia San Quintin, 1 mile inside bay from Punta 

 San Quintin, Apr. 



Inasmuch as the Mexican material is virtually identical with the type 

 and is on the same host, the description above has been modified only 

 slightly from Drew's original one. 



Acrochaetium spicuHphilum sp. nov. 

 Plate 10, figs. 2-4 



Thallis endozoicis, in circumque spicula spongiae (Haliclonae) flor- 

 entibus, in hospitem penetrantibus 1-2 mm., repentibus, stricte adhaer- 

 entibus, irregulariter ramificatis, superimpositis compactisque constanti- 

 bus ; cellulis formae irregularis 3-6 p, diametro ; chromatophorio parietali. 



Thalli endozoic, forming reticular red patches on and in a sponge; 

 vegetative filaments growing on and around the spicules and penetrating 

 to a depth of 1-2 mm. within the reticulations of the host, creeping, 

 closely adherent and following the spicular reticulations closely, irregu- 

 larly branched, becoming superimposed and compacted producing short, 

 branched, erect or semi-erect free filaments of 2-7 cells at the surface, 

 and sometimes within; cells of inner vegetative filaments of irregular 

 shape, often at first elongate, becoming rounded and in compacted parts 

 angular, 3-6 [x in diameter; ceils of free filaments ellipsoid to ovoid, 4-6 

 IX in diameter; chromatophore parietal; reproduction apparently by 

 monospores arising by modification of cells of the short free filaments, 

 but these not positively identified. 



Type: Holotype is Dawson 9672, April 1951, in vial 2294 and on 

 slides 1688-1689 in HAHF. 



Type locality: In a fragment of a sponge of the genus Haliclona 

 from drift, Bahia de San Quintin, just 1 mile inside end of peninsula. 



This species is readily distinguished from the other sponge-inhabiting 

 Acrochaetium, A. spongicolum Weber van Bosse (1921, p. 195, figs. 56- 

 57) by the bright red, reticulate appearance of its colonies, its creeping 

 habit, and superimposed filaments which form a thick covering over the 

 spicules to a considerable depth within the host. Although reproductive 

 material is not available for comparison with the peculiar Rhodochor- 

 tonopsis spongicola Yamada (1944, p. 23, figs. 7-8), our plant seems 

 distinct in its compactly superimposed horizontal filaments. 



