REPORT ON THE HYDROIDA, 3 
genera now specially constituted for their reception. Many are of great interest in the 
light they throw on the external morphology of the group, and in the aid which 
they afford towards a philosophic conception of the significance of parts otherwise 
enigmatical. 
I believe, therefore, that the value of the collection will be enhanced, and its 
instructiveness made more available if the technical description of the species be preceded 
by a few introductory remarks on the general morphology of the Plumularidz, more 
especially on such points as receive important illustration from the species described in 
the present Report. 
GENERAL MorPHOLOGY OF THE PLUMULARIDA. 
The Plumularidz constitute a very natural section of the Calyptoblastic Hydroids. 
Their hydrothecz are always sessile, and are carried on one side only of the supporting 
ramulus. Nematophores of a definite form, and with a definite arrangement, are always 
present. The gonangia are either fully exposed and destitute of any special protective 
apparatus, or they are enclosed or otherwise protected by more or less modified portions 
of the hydrocaulus.* 
The Plumularide admit of division into two primary sections, characterised by the 
condition of the nematophores. In one—the Eleutheroplea (Pls. I, II., &c.),—the 
nematophores are attached only by their proximal end, and in almost every case are to a 
certain extent moveable on their point of attachment. In a very few instances the 
moveable nematophores are associated with nematophores of the fixed type (PI. VIII. 
figs. 1-3). 
In another section—the Statoplea (Pls. XL, XII, XIII., &c.)—the nematophores are 
adnate to the chitinous periderm for a greater or less portion of their length, or are fixed 
by a base too wide to admit of movement on the surface of attachment. No nemato- 
phores of the moveable type ever occur in this section. 
Each of these sections admits of a further division into two main groups—the 
Phylactocarpa (Pls. XI., XII, XIIL, &c.),” in which the hydrocaulus has become modified 
so as to form a more or less complete protection for the gonangia, and the Gymnocarpa 
(Pls. If., IIL, IV., &e., and Pl. VIII. and Pl. XIX. figs. 1-3), in which no protective 
apparatus is present. 
1 For definitions of the terms here used see p. 17. 
2 'The collection contains no example of the phylactocarpal Eleutheroplea. For our knowledge of the occurrence 
of phylactocarpal forms among the Eleutheroplean Plumularidz, we are indebted to Mr. J. Walter Fewkes, who detected 
the presence of this condition in two Hydroids, Hippurella annulata and Callicarpa gracilis, obtained by the dredge of 
the U.S. Coast Survey Steamer “Blake.” Bull. Mus. Comp. Zool., loc. cit. 
