90 UNITED STATES NATIONAL MUSEUM BULLETIN 251 



Gilbert Islands : Onotoa Atoll : P. E. Cloud, sta. GOC-55. One colony (USNM 

 11492). 



Description. — Seven colonies from the Palau Islands and a single 

 somewhat multilated one from the Gilbert Islands were examined. 

 The largest colony is 23 mm. X 10 mm. in extent and less than 1 mm. 

 in thickness. Test gelatinous, transparent, and contains some crystal- 

 line needles (fig. 30e) in the specimen from the Gilbert Islands, but 

 many stellate sjiicules of 22-38ju, (32/^ on an average) in diameter in 

 the Palau specimens. Spicules resemble closely those of D. moseleyi^ 

 10-15 rays (about 12 on an average) on equatorial plane and short, 

 stout and pointed rather sharply at tip. Number of spicules differs 

 considerably according to colonies ; distributed with moderate density, 

 evenly throughout the test from bottom to surface in some colonies, 

 while in others they are arranged in only a single layer, less densely 

 along the upper edge of the zooidal stratum, quite sparsely in other 

 parts of the colony. Some colonies only sparsely impregnated with 

 spicules may contain spicules somew^hat larger than those in densely 

 impregnated colonies. Superficial spiculeless layer well defined. 

 Well-developed hypozooidal lacmiae in test so spacious that zooidal 

 stratum and thin bottom layer are merely connected along periphery 

 of colony and at other places where a few zooids are situated verti- 

 cally; in other portions zooids are all horizontal in zooidal stratum, 

 with dorsal sides down so that atrial apertures open to hypozooidal 

 lacunae (fig. 30c). Dark bluish pigments are deposited in elongated 

 cells in the surface layer of the zooidal stratum, or scattered throughout 

 the whole zooidal stratum; sometimes pigment cells occur at some 

 parts of the colony forming nearly spherical masses measuring about 

 0.5 mm. in diameter. Due to these pigment cells, entire colony usually 

 a grayish or dark bluish mass with a whitish margin. Frequently 

 pigment cells are missing above respective zooids and consequently 

 the dark colored colony surface is sprinkled with a number of white 

 spots (figs. 30a, h). Common cloacal apertures elliptical. 



Thorax 800-1200/x, abdomen nearly as long as thorax, usually about 

 900/x in length. Zooids brownish in some colonies, seen through the 

 test where spicules are veiy sparse. No sj^stem found in arrangement 

 of zooids. Atrial aperture opens at level of third stigmatal row 

 and its shape varies according to degree of contraction; it is con- 

 siderably wide, roundish in shape, and does not form any siphon in 

 some colonies, while a short but distinct siphon is formed in others. 

 About 10 longitudinal muscles on each side of thorax. Stigmata 8 to 

 10 in each of four rows, 8 tentacles, dorsal languets roughly triangular 

 in shape. Hind stomach and midintestine very distinctly defined. 

 Generally intestine is not so strongly curved as in Didemnum {Didem- 

 num) . Anus opens at dorsoposterior corner of thorax, margin plain. 



