64 UNITED STATES NATIONAL MUSEUM BULLETIN 251 



indiscernible; only in the specimen from the Galapagos Islands is it 

 somewhat prominent. The common cloacal apertures are about 2 mm. 

 in diameter in larger examples and may be fringed with several lobules 

 as shown in a Hawaiian specimen (fig. 20a) . Usually, the spicules are 

 distributed densely and evenly throughout the colony from the bottom 

 to the surface, although they are rather sparse in the colony from the 

 Galapagos and in some from the Palau Islands — especially so above 

 the zooids in the latter. The spicules may reach 35-48/a in diameter as 

 in the Hawaiian and some Palauan specimens, although they are usu- 

 ally much smaller, for instance, 16-l7jii to 22-24jli in diameter in many 

 specimens from the Palau Islands. Their rays are short, delicate, and 

 very numerous, usually more than 20 on the equatorial plane; rarely a 

 few spicules are found with somewhat fewer rays, 12-15 on the equa- 

 torial plane, in some colonies from the Hawaiian and Palau Islands. 

 Some colonies contain worn spicules quite spherical in shape and with 

 a fine areolate appearance on the surface. The color of the colonies 

 varies from pure white to bright carmine red or sometimes tinted 

 purplish; this coloration fades very quickly in preservation. Pre- 

 served colonies are snowy white, grayish white, pale yellowish brown, 

 faintly yellowish gray, pale greenish gray, pale orange, or even dark 

 purplish brown in color. Pigment cells are deposited most densely 

 in the surface layer of the zooidal stratum, corresponding to the tho- 

 racic layer, but generally are missing in the abdominal layer and along 

 the periphery of the colony. On the purplish-brown colony from the 

 Palau Islands, encrusting Polycarpa cryptocavpa (Sluiter), pigment 

 cells are missing in small oval or elongated areas surrounding the 

 branchial apertures in some parts of the colony and consequently the 

 surface of the test shows a kind of spotted appearance (fig. 20&). 

 Hypoabdominal lacunae absent. 



Zooids rather small and sometimes stained dark grayish or brown- 

 ish. Larger abdomens may reach GOOju, in length. Branchial 

 aperture 6-lobed, atrial aperture very wide and without any languet; 

 retractile muscle usually short, but may be as long as contracted throax 

 in some zooids. About 7 stigmata in each of 4 stigmatal rows. Usually 

 a single testicular follicle in zooids from the colonies from the Philip- 

 pine, Galapagos, Hawaiian, and Palau Islands, while 2 or 3 follicles 

 were found in the specimens from the Gilbert Islands; in the latter 

 one of the 11 zooids examined had a single follicle, nine had 2 follicles 

 and the rest 3 follicles. The proximal part of vas deferens coils 4-5 

 to 8-9 times. The general structure of the zooids conforms well 

 in detail with that of common didemnids. 



Four pairs of ampullae present in larvae. 



