190 
most of them being about half again as long as wide; its distal 
portion is not serrate; P, is 17 mm. long with twenty-six joints, 
the first six squarish, then gradually becoming elongate and about 
twice -as long as broad distally; this pinnule is somewhat stouter than 
the preceding, and while tapering evenly to the tip, is not flagellate. 
Colour (in spirits). — Light yellow. 
The short intersyzygial interval of this form is its most striking 
character, and is a point of especial interest as the intersyzygial 
intervals in Heliometra, and, in fact, in almost all of the Antedo- 
nidæ, are remarkably true to species. 
Genus Erythrometra A. H. Clark. 
Erythrometra 1908. A. H. Clark, Proe. Biol. Soc. Washington, Vol. 21, 
p. 126. 
Erythrometra ruber (A. H. Clark). 
Antedon ruber 1907. A. H. Clark, Proc. U. S. Nat. Mus., Vol. 88, p. 146 
Erythrometra ruber 1908. A. H. Clark, Proc. Biol. so Serraleh 
Vol. 21, p. 127. 
South of the Goto Islands; 32902' N. lat., 128945' 
E. long.; 105 fathoms; Suensson, May 12, 1898. One 
small specimen, with arms 25 mm. and cirri 5 mm. long. 
Genus Mastigometra A. H. Clark. 
Mastigometra 1908. A. H. Clark, Proc. Biol. Soc. Washington, Vol. 21, 
p. 229. 
This is the genus which is most nearly related to Antedon 
of the Mediterranean and western European coast, the most obvious 
difference being that P, is nearly or quite three times as long 
as P,, and P, is similar to P, and half again as long as P3, 
whereas in Antedon P, is twice as long as P,, the latter being 
of the same length as P, and the following pinnules. Although 
comparatively slight, this difference is perfectly constant, none of 
the four species of Antedon showing any approach to Mastigometra, 
and either of the species of Mastigometra exhibiting any tendancy 
to approach Antedon. It is an interesting fact that the specific 
differentiation within the genus Mastigometra is almost an exact 
