164 



BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



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and position. The surface is very uneven, with deep irregular folds 

 and shallow depressions, and is usually quite thickly incrusted with 

 sand, small fragments of shells, e'c. These also occur to a consider- 

 able extent in the deeper parts of the colony. Dimensions of two of 

 the largest specimens: 67 mm. long by 42 

 mm. wide, and 76 mm. long, 25 mm. high, 

 and 18 mm. in greatest width. Test brownish, 

 opaque, of a somewhat fibrous appearance, 

 quite hard in the alcoholic specimens, though 

 not very tough. 



Zooids irregularly distributed, not very 

 numerous in proportion to the amount of test 

 substance. They are slender, the post-abdomen 

 (which is very narrow) constituting over 

 half their total length when well developed. 

 Such zooids, even in the contracted state, may 

 reach 8 or 9 mm. in length. Branchial aper- 

 ture with six rather long lobes ; atrial aperture 

 on a low papilla on the anterior dorsal part of 

 the thorax; ordinarily it is not lobed. Both 

 apertures with strong sphincter muscles. A 

 long, narrow atrial languet arises a little dis- 

 tance anterior to the atrial papilla. The lan- 

 guet may or may not be cleft into two or three 

 lobes at its tip. (See different forms shown 

 in fig. 112.) 



Mantle musculature forming slender but 

 distinct longitudinal bands on the thorax; on 

 the ventral portion of the latter a deeper layer 

 of transverse fibers can also be distinguished. 

 Tentacles rather few, of two sizes placed 

 alternately. 



Dorsal languets rather small, borne on the 

 transverse vessels of the left side at a distance 

 from the median dorsal vessel equal to the 

 width of about four stigmata. 



Branchial sac long and narrow, the trans- 

 verse vessels conspicuous^ 7 muscular. About 

 20 rows of stigmata, with 11 to 14 in a row on 

 each side. In several zooids the writer found 

 the lesser number to prevail on the right and the greater on the left 

 side. The stigmata do not commence very close to the endostyle, and 

 those near that organ are successively shorter in their dorso-ventral 

 diameter; those near the median dorsal vessel are also slightly short- 



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Fig. 112. — Amaboccium 



CltATERIFERUM S L D I - 



ter. zooid. x 17.5. 

 The small figures 

 show variations in 

 the form of the 

 atrial lanodet. 



