On the Anatomy of an Arenaceous Polyzoon. 9 



particles, but sometimes it springs direct from the sub- 

 stratum on which it grows. 



It is, as a rule, dichotomously branched, and the branches 

 come off in many planes. The ramification is very profuse, 

 which gives to the whole colony a reticulate appearance, but 



1 have not succeeded in detecting any actual anastomoses. 

 The fully grown sandy nodes are spherical, and usually 



about 1 mm. in diameter. They are perfectly distinct from 

 one another, and the internodes are well developed, being a 

 little shorter than the diameter of the nodes. The terminal, 

 young nodes are much smaller than the older, fully grown 

 ones. 



The polypides have up to 12 tentacles, although sometimes 

 it is possible to count only 10 or 11. In the living animal 

 the fully expanded tentacles are about 2 mm. long. 



In one slight varietal form (Fig. 3) the nodes are 

 somewhat larger and nearer together than in the typical 

 form. It is this slight variety which I was able to examine 

 in the living condition, and from which the anatomical 

 figures are drawn. 



Cryptozoon concretum. 



The zoarium (Fig. 4) forms dichotomously branched 

 tree-like masses, provided with a common sandy base. The 

 entire growth is very much coarser than in C. wilsoni, and 

 the branching, which takes place in several planes, is less 

 copious and intricate. Sometimes, but only rarely, the 

 branches appear to form anastomoses. 



The internodes are reduced almost to nothing, and the 

 nodes usually touch one another, or are actually fused 

 together. It is only in the upj^er, younger portions of the 

 colony that separate spherical nodes can be distinguished. 

 In the lower, basal portions, they fuse together into common, 

 stem-like, sandy masses. The diameter of a stem, near the 

 base of a colony and above the basal expansion, is about 



2 mm. ; while the nodes which are in process of fusion and 

 still separate gradually decrease in diameter as they 

 approach the ends of the branches. The polypides are 

 larger than in C. wilsoni, their tentacles being 3 mm. long 

 in the fully expanded, living animal. The number of the 

 tentacles is 14. The dift'ereutiation of the stomach, into 

 digestive and non-digestive regions, is somewhat more 

 strongly marked than in C. wilsoni. 



