i6 



a 6"> slender one in the centre. These branches send off one or two pairs of usually opposite 

 branchlets, the first pair being from 8 to lo mm. from the bases, the second pair being 9 to 

 10 mm. above the first. Above these pairs an occasional lateral branchlet is produced, especially 

 toward the distal ends of the branches. Some of the branchlets, however, are simple throughout 

 their length of as much as 1 2 cm. The branches arise from horny nodes. The calcareous inter- 

 nodes vary in length from the second, which is 3 mm. long, to a length of 14 mm. on the 

 terminal branchlets. The horny nodes vary from the ba.sal one of 2 mm. to about .2 mm. on 

 the terminal twigs. 



The diameter of the main stem near the base is 2.5 mm., decreasing to a thread-like 

 axis on distal branchlets. The calyces tend to a biserial arrangement on the branches, but are 

 much more thickly emplanted on distal parts. On the tip of one branch they are thickly 

 emplanted over the surface of an oval object which is probably a parasitic barnacle. The 

 branches are erect, forming a symmetrical and graceful colony. 



The individual calyces are club-shaped, and inclined toward the distal end of the colony, 

 sometimes with the adaxial wall contiguous with the branch throughout. 



Their adaxial side measures about 2 mm. in length, and their abaxial about 3 mm. 

 Diameter at margin i.i mm., at base about .8 mm. The calyx walls are filled with large and 

 small spindles, many of them spirallj- arranged and more or less bent or wavy. Some of them 

 attain a length of 2.1 mm., or even 3 mm., extending the whole length of the calyx from 

 base to summit. These larger spicules are usually placed on the abaxial wall of the calyx, and 

 sometimes they occur in two series forming a sort of rude inverted chevron on the abaxial wall. 

 There are a few similar but smaller spindles arranged vertically on the adaxial side. While the 

 points of the spindles often extend beyond the margin, they do not form a regular series of 

 eight marginal points such as is found in many other Isidce. 



The tentacles are armed with numerous bar-like spicules irregularly placed, but most 

 often transversely disposed. 



The coenenchyma is thin, and contains a few of the large spindles longitudinally disposed, 

 and more numerous small, bar-like forms. 



Spicules. These have already been described. Their maximum length, 3 mm., agrees 

 with Verrill's description of A. noj'inani \ but the manner of branching seems quite distinct. 

 The surfaces of the spicules are covered with fine conical points, evenly distributed. 



Color. The colony is white, in alcohol, with the polyps a very light golden brown. 

 The horny nodes of the axis are dark golden brown. 



This species is doubtless nearest A. norniani Verrill; but a direct comparison of the 

 Siboo^a material with a specimen identified by Verrill as A. norniani shows that A. iveberi 

 differs from A. norniani in the shape of the calyces, which are much longer and more slender 

 in A. norniani\ and in the spicules, which are much more slender and form a regular crown 

 of points in A. norniani. 



' Bulletin of Museum of Comparative Zoology, XI, N" I, p. 17. 



