8 



the calcareous substance of the axis shows a crystalline appearance, there are no indications 

 that it is composed of fused spicules. The concave sides of the cross section correspond, of 

 course to the grooves for the primary canals, and the number eight seems significant as being 

 the original number of these canals, corresponding to the eight intermesenterial chambers of 

 the primary polyp of the colony or branch. The central area is marked by an axial nuclear 

 spot, from which many lines radiate toward the periphery of the area 



The horny nodes are hour-glass shaped, in longitudinal section, their ends being concave 

 for the insertion of the convex ends of the calcareous internodes. At the line of juncture there 

 is an irregular mass of horny projections alternating with the calcareous material, giving an 

 anchorage that binds the node and internode together. There are no calcareous spicules in 

 the nodes. 



Spicules. These are all quite small, and of several forms. All are modifications of 

 short tuberculate spindles. Double spindles, dumb-bell shapes, double heads, crosses and densely 

 tuberculate oval forms predominate. All are closely tuberculate, and most of them show a 

 median, constricted smooth girdle. There are a few double crosses and spindles with regular 

 whorls of tubercles. 



Color. The specimens in alcohol are a tan brown, the dried specimens being darker 

 brown. Axis white, with the horny nodes dark horn brown. 



General distribution. This species has been reported from the Indian Ocean, and 

 parts of the tropical eastern Pacific. The form reported from the Mediterranean is in all 

 probability not this species or genus. 



This species is quite variable, and specimens differ much according to size and age, the 

 larger stems and branches having the "moniliform" appearance that has led some authors to 

 describe several species on the basis of what appears to be merely varietal differences. 



Many of the dried specimens were originally much larger than the one described ; but, 

 owing to their excessive brittleness, they are so badly broken up that the original dimensions 

 can not easily be ascertained. 



2. Isis reticulata new species. (Plate I, figs. 2, 2#; Plate V, fig. 2). 



Stat. 273. Anchorage off Pulu Jedan, East coast of Aru Islands. 13 meters. Sand and shells. 



Colony much broken up, the specimens consisting of large and small fragments all from 

 the same station. General habit loose and straggling, much less inclined to the formation of 

 dense tufts than in Isis h^pp^lris. The thickest stem found is 7 mm. in diameter, and the horny 

 internodes are almost entirely obliterated, being indicated by darker color alone. The longitudinal 

 grooves are continuous over the calcareous and horny joints, the latter being but slightly con- 

 stricted. The first calcareous internode is i cm. long, the next 1.6 cm., the next 2 cm., and 

 bearing a branch a little above its middle. Further up the horny nodes are sharply constricted, 

 clearly defined and about 2 mm. in length. The branching is straggling, and there are occasional 

 anastomoses of branches. There is a distinct tendency toward a flabellate form of colony. The 



