Mr. W. K. Fisher on Asteroidea. — 171 
Beyond a certain similarity due to the outward form, 
particularly to the slender rays, the Linckiide have little 
claim to this genus. 
The presence of intermarginal plates and of single am- 
pulle, and the absence of actinal intermediate plates, and of 
interbrachial septa with calcified pillar, will debar Metrodira 
from the Asteropide, Ganeriide, and Poraniide, while 
additional differences in the abactinal skeleton make the last 
two families unsuitable homes. 
Even the Echinasteride appear to be incompatible. The 
abactinal plates of Metrodira are tessellated, not at all reticu- 
late, while the marginal plates are large, compact, and form 
a vertical side to the ray. The interbrachial septa are almost 
lacking. 
It seems better to place this genus in a separate family 
rather than to enlarge the Echinasteridz and, in a measure, 
spoil its homogeneity. The case of Metrodira is much like 
that of Acanthaster, Mithrodia, and Valvaster, which have at 
one time or another been in the Echinasteride. 
Metrodiride, new family. 
Characters.— Whole skeleton overlaid by a rather thin skin 
partially obscuring the outlines of the plates ; rays slender ; 
abactinal plates tessellate, partly imbricated, with small 
spines; marginal plates large, forming side-wall of ray, there 
being one or more series of intermarginal plates on the 
proximal part of ray ; actinal intermediate plates reduced to 
one, between mouth-plates and inferomarginals; papule 
isolated, strictly abactinal; tube-feet with sucking-disk 
devoid of calcareous deposits ; ampulle single ; interbrachial 
septa rudimentary, practically absent. 
Priamaster, Keehler*.—This genus, founded on Priam- 
aster magnificus, Koeller, is very close to (Gephyreaster, 
Fisher f, type Mcmaster swift’, Fisher, North Pacific Ocean. 
Priamaster has much wider ambulacral furrows, quadriserial 
and very large tube-feet, and small actinal intermediate areas. 
The arrangement of spines on the mouth-plates of Gephyre- 
aster is very characteristic, and is figured (loc. cit. pl. lvil. 
fig. 2), The abactinal paxilliform plates of Przamaster, the. 
* Zool. Anz., Feb. 18, 1912, p. 157; Deuziéme Exp, Antarctique 
Francaise, Echinodermes, 1912, p. 91, pl. viii. figs. 1, 3, 8. 
+ Ann. & Mag. Nat. Hist. ser. 8, vol. v., Feb. 1910, p. 171; Asteroidea 
of the North Pacific ete., 1911, p. 175, pl. xxx. figs, 1-4, pl. lvu, figs, 2, 
2a-c, pl. lix, figs. 5, 5 a. 
Lae 
