10 AMERICAN HYDROIDS. 



protection often afforded by tbe sarcostyles. In expansion, the hydrantbs of tbe Eleutberoplea 

 seem, as a group, to be capable of greater extension beyond tbe orifice of tbe bydrotbeca than 

 those of the Statoplea. They are seldom brilliantly colored. Indeed, I know of no American 

 species which is at all notable in this direction. While working in Naples, however, I saw a 

 species of Antfunulnriii that was rendered quite striking by the brilliant rose-red color of the 

 bodies of the hydrantbs. Aglnopln'iiiti tubulifera often displays a rather bright yellow color that 

 extends to the hydranths. Several species of Lytocarpus are remarkable for having the cceuosarc 

 of both stem and hydranths packed almost full of granular black bodies, which give a very dark 

 color to these parts. I have been unable to determine tbe nature of these peculiar granules, but 

 they seem to be confined to the species of this genus, and are found in all comparatively fresh 

 specimens examined by me. The hydranths of several species of Aglaophenia, notably an uncle- 

 scribed species studied at Naples, are colored green from the innumerable unicellular alga' with 

 which their tissues are packed. In a majority of plnmularians, however, the polyps are either 

 colorless or. rarely, have a brownish tinge when alive. Their size is not very great, averaging 

 about the same as those of the Sertularidie. 



Hydrotheca'. These are always sessile and usually have their posterior side partially or wholly 

 attached to the hydrocladia. In Aglaophenopsis hirnuta (Plate XXIX, fig. 12) the proximal hydro- 

 theca' are almost entirely free and the distal hydrotheca' largely aduate. In Schizotrirha tenvlla, 

 also, the hydrotheca' are nearly free, a condition often seen among Australian forms of Plnmiilaria. 

 As a rule, they are much more closely approximated in the Statoplea than in the Eleutheroplea, 

 although riumularlu demlritini (Plate VI II, tig. 4), Monoxtwhax tiitadridi-im, Diplopti-ron grande, 

 and D. loii</i)>i>iii<i, eleutheroplean forms, have the hydrothecife as closely approximated as in the 

 statoplean Gladocarpus flexuoswi, C. bispinosus, and Aglaophenopsis dintann. In form and com- 

 parative size the hydrotheca- of the Plumularida' differ very widely. Among the Eleutheroplea 

 many species are much wider than deep as in 1'lnmitlttria lugririfera (fig. 8), Antennopsis longicomti, 

 A. iiit/ni (tig. 10), while they are more than twice as deep as wide in JHploptcron graiide (fig. 0) and 

 Cnllicdrpa gracilix. Among the Statoplea almost as great divergence is found between Halicorii- 

 opxis aricularix Kirchenpauer, on the one hand, and Cludocarpus flexuosux (fig. 25), on the oilier. 

 In comparative size the divergence is still greater, as will be seen by comparing Antennopsis nigra 

 (fig. 10) with lUploptcron ijrantle (fig. 9) among the Eleutheroplea, and Aglaophenia latirostris (fig. 

 21) with Cln-iloiKirpun grandis (fig. 28) or C. partidisea among the Statoplea. 



The aperture of the hydrotheca is often horizontal or at right angles with the hydrocladial 

 axis. Sometimes, however, it is vertical, as in CludocurpKn carinatiis (fig. 30) and Aglaophenia 

 sarlgnyfina; but ordinarily the opening is inclined between these extremes. In DiplocJieilus 

 mirubilis Allman the hydrothecal wall is rolled over, as it were, the margin forming thus a double 

 wall throughout the upper part of the hydrotheca. 1 In a few species there is an anterior keel to 

 the hydrotheca, as in Hitlopteris carinata (i late XVII, fig. 8) and Cladocarpus carinatiis (Gg.SQj. 

 This structure, is produced into a very conspicuous process reaching far beyond the hydrotheca 

 in Aglaophenopsis cor nut a (fig. 33). 



The margin is almost always plain or destitute of teeth in the Eleutberoplea, the only exception 

 known to me being Gultija hum ilia Allman (Plate XVII, fig. 10). This genus, however, is almost 

 exactly intermediate in structure between the two great groups of the Plumularidae, although 

 agreeing more nearly with the Eleutheroplea. The margin of the hydrotheca' of this latter group, 

 although always toothless, with the exception noted above, is often characterized by more or less 

 pronounced siuuations, as in rininulurtu filicaulis (fig. 18). The condition of affairs is exactly the 

 reverse among the Statoplea, where a plain margin, as found in Cladocarpus jwurtalexii (fig. '>!), 

 Nnditlii'f/i iliilti. (fig. 35), and a very few other species, is the exception. There are almost always 

 either teeth or siuuations, the latter being especially characteristic of several species of Haliror- 

 narin. A few forms have one or two prominent anterior teeth varying considerably in shape. 

 The most common arrangement among American species is that found in Aglaophenia rigida 

 (Plate XVIII, fig. -'5), which has nine even, conspicuous, pointed teeth. A number of Pacific coast 

 species exhibit a departure from this in the direction of unequally developed teeth, some of which, 

 usually the anterior, are bent abruptly inward or outward. Lytocarpus furcatux (tig. 36) is 



Mali- snys that (liis structure is merely a very fjreat thickening of the distal portion of the hydrothecal wall. 



