REPORT ON THE HYDROIDA. 31 
Polyplumaria pumila, n. sp. (Pl. IV. figs. 7, 8). 
Trophosome.—Colony attaining a height of one or possibly two inches ; stem strongly 
fascicled and giving off opposite pinne, which do not carry hydrothecze, and are also 
fascicled ; hydrocladia alternate, scarcely exceeding one-twentieth of an inch in length, 
borne on the main stem and primary pinne, each giving off its accessory ramulus from a 
point close to the base of the proximal hydrotheca ; hydrothecal internodes continuous. 
Hydrothece cylindrical, rather distant, adnate only by their base to the rachis, and with 
the internodes which support them carrying besides the lateral nematophores a single 
mesial nematophore at the proximal, and another at the distal side of the hydrotheca. 
Gonosome.—Gonangia pyriform, with obliquely truncated summit. 
The specimens were fragmentary, and did not afford sufficient evidence of the size 
attained by the perfect colony ; but it is probable that it reaches a height of between one 
and two inches. Itis thus a very much smaller, and altogether more delicate species than 
the Diplopteron insigne of the “ Porcupine,” which attains a height of about six inches. 
The accessory ramuli carry one, two, or three (possibly in some cases more) hydrothece, 
and have a rather long proximal internode, which is always destitute of hydrotheca. 
I was unable to find in the present species the second pair of minute lateral nemato- 
phores which in Polyplumaria (Diplopteron) insignis is developed at the distal side of 
the hydrotheca. Polyplumaria pumila is further distinguished from Polyplumaria 
insignis by the more cylindrical form of the hydrothece, which do not present the slightly 
everted margin which gives a somewhat campanulate form to the hydrothecee of 
Polyplumaria insignis. All the known species are doubly pinnate. 
The gonangium is borne on a short cylindrical peduncle, and has a truncated summit 
and a short transverse segment at its very much contracted base. 
All the species as yet discovered are inhabitants of the deeper sea zones. 
Dredged at Station 75, July 2, 18738; lat. 38° 37'N., long. 28° 30’ W.; depth, 450 
fathoms ;. bottom, sand. 
Heteroplon, nov. gen. 
Name, from érepos, dissimilar, and ézAov, a weapon, in allusion to the presence of two different 
kinds of nematophores. 
Generic Coaracter. Z'rophosome.—Hydrocladia pinnate ; hydrothecal internode with 
the lateral nematophores moyeable, and with a mesial fixed spine-like nematophore below 
the hydrotheca. 
Gonosome not known. 
The genus Heteroplon combines the characters of the Eleutheroplean with those of 
the Statoplean Plumularide. The hydrothece are flanked each by a pair of moveable 
nematophores of precisely the same kind as in the typical Eleutheroplea, while the mesial 
