156 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



?1909. Didemnum margaritiferae Hartmeyer, Bronn's Tier-reich, vol; 3, 



suppl., p. 1450. . 



1909. Polysyncraton dubium Sluiter, JMoj/a-Exped., vol. 56b, p. 69, pi. 4. 



figs. 3 and 3a ; pi. 7, fig. 10. 

 1912. Polysyncraion- dubium Habtmeyeu, Deutche Tiefsee Exped., vol. 16, 



p. 325. 



Colony flat and incrusting, but rather thick and fleshy. Surface 

 fairly smooth and even except in a specimen from station D513G, in 

 which it has deep convoluted furrows, and in one from station 

 D5555, in which it is raised into low rounded elevations separated 

 by furrows. Exterior of the colony varying from smooth and shiny 

 to minutely granular, according to the abundance of spicules in 

 the superficial part. Branchial orifices of the zooids conspicuous 

 where the spicules are abundant, but less noticeable where they are 

 scarce. Common cloacal orifices when distinguishable large and few 

 in number, sometimes apparently only one or two for the entire 

 colony. Color a pale, slightly reddish buff, except in the case of one 

 specimen from station D5150, which is blackish, owing to the abun- 

 dant presence of bluish-black pigment, contained chiefly in irregular 

 elongated branching cells in the test. Greatest diameter of largest 

 colony, 59 mm. Thickness usually ranging from 3 mm. to 8 mm., but 

 in some places it may be less or greater than these measurements. 

 One specimen (from station D5145) grew on the shell of a small 

 living crab, arching over and inclosing the carapace so as to leave 

 only the limbs and mouth parts uncovered. 



Test yellowish, gelatinous, but moderately tough; its cells free 

 from conspicuous pigment except in the specimen above mentioned. 

 Bladder cells abundant. Spicules few in the interior and lower por- 

 tions of the colonies, but often very thickly distributed in the super- 

 ficial layer. They are usually mostly moderately large, 0.25 to 0.04 

 mm. in diameter, and the typical form appears to be regularly stel- 

 late, with a moderate number of smoothly tapering conical points 

 ending in fairly sharp extremities. Such spicules are the chief kind 

 occurring in the colonies from stations D5150 and D5139. In the 

 colony from station D5145 they are accompanied in some parts of the 

 test by spicules with more or less blunted or truncated rays, while 

 in the colonies from stations D5174 and D5555 none of the spicules 

 have the regular conical points, the points being in all cases more or 

 less truncated, or at least not of regularly tapering conical form. In 

 the last two cases the rays of the spicules are very much more numer- 

 ous than in the others. The spicules in the colony from station D5174 

 average smaller than the usual dimensions; in that from station 

 D5555 they average larger, many reaching 0.05 mm. in diameter. 

 These different forms of spicules are shown in figure 107. 



