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 Plumularidse, more 

 especially on such points as receive important illustration from the species described in 

 the present Eeport. 



General Morphology of the Plumularid.e. 



The Plumularidse constitute a very natural section of the Cal}qDtoblastic Hydroids. 

 Their hydrothecse 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 Plumularidae admit of division into two primary sections, characterised by the 

 condition of the iiematophores. In one — the Eleutheroplca (Pis. 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 (Pis. 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 (Pis. XL, 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 

 (Pis. II., III., IV., &c., and PI. VIII. and PI. 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 Plumularidse, we are indebted to Mr. J. Walter Fewkes, who detected 

 the presence of this condition in two Hydroids, Hippurella amndata and Callicarpa (jranlh, ohtained hy the dredge of 

 the U.S. Coast Survey Steamer " Blake.'' Bull. Mas. Comp. Zool., loc. cit. 



