REPORT ON THE POLYZOA. 
169 
fact difficult to draw an}* definite line between them. In the sense in which the name 
is here employed, it is extended to embrace continuous zoaria, usually composed of 
cylindrical branches, for the most part of uniform diameter throughout, and in the more 
typical species obtusely rounded at the ends, towards which alone the orifices remain 
patent, the lower parts becoming more or less solidified and sometimes presenting no 
trace of the zocecial structure either externally or internally. 1 In the less typical forms 
this condition does not attain to anything like the same extent, but in all there is a 
very great tendency to the obliteration of the zooecia in the older parts. 
Another circumstance in which the true or typical species of Myriozoum are distin- 
guished from the rest, is the finely cancellated structure of the walls of the cells, or as it 
may be stated, of the entire substance in the actively growing parts. On the exterior 
this is indicated by the close reticulation, as it may be termed, rather than punctuation of 
the surface, whilst internally the walls of the zooecia are generally very thick and finely 
cancellated, so that ample provision is made for the ready diffusion of fluid throughout 
the growth ; which may not improbably be connected with the abundant deposit of 
calcareous matter in the older portions of the zoarium. 
These differences in essential structure appear to be of sufficient importance to 
justify, if not the entire separation generically of the typical forms from others here 
included in the genus, at any rate the placing of them in a distinct section, as 
follows : — 
§ 1. Myriozoa typica. 
(1) Myriozoum truncatum, Donati. , 
(2) Myriozoum subgracile , d’Orbigny. 
(3) Myriozoum coarctatum (Sars). 
§ 2. My riozoa dubia. 
(1) Myriozoum honolulense, n. sp. 
(2) Myriozoum immersum, n. sp. 
(3) Myriozoum simplex, n. sp. 
(4) Myriozoum marionense, n. sp. 
All the forms in the Challenger Collection belong to the second division. 
1 When a portion of the completely solidified part of Myriozoum truncatum is decalcified, the chitinous opercula and 
shrunken remains of the endocyst may often he found enclosed in the interior. 
(ZOOL. CHALL. EXP. — PART XXX. 1884.) Gg 22 
