i6 



slender one in the centre. These branches send of) one or two pairs of usually opposite 

 the first pair being from 8 to 10 mm. from the bases, the second pair being g to 

 mm. above the first. Above i1k-m- pairs an occasional lateral branchlet is produced, especially 

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

 is much as 12 cm. 1 h< ■ branches arise from horny nodes. The calcareous inter- 

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

 terminal branchlets. Hu- horny nodes vary from the basal one of 2 mm. t<> about .2 mm. on 

 the terminal tw 



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

 a\is 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 1.1 mm., at base about .8 mm. The calyx walls are filled with large and 

 small spindles, many of them spirally 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. YVhile the 

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

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



The tentacles are armed with numcrous 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. normani ', 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. normani Verrill; but a direct comparison of the 



Siboga material with a specimen identified by Verrill as A. normani shows that A. weberi 



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



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



toints in A. normani. 



Museum of Comparative Zoology, XI. N" i, p. 17. 



