THK PLUMULARIDjE. 13 



dautly iii the hydrocladia of many species of I'lHtulnri<t, ('In<to<-rpu8, .and otlu-r genera. Tliese 

 septal ridges can hardly be regarded as a result of the bending of the internode.s in which they 

 are found, but seeru rather to be formed by annular thickenings produced by the addition of 

 chitine that is, the septal ridges are actually built up of new material and not formed by folds 

 in the existing structures. Ju the same way, in the writer's opinion, the ordinary posterior 

 intrathecal ridge is formed by the addition of a quantity of chitine, which constitutes an entirely 

 new structure, and not by a fold in the existing hydrothecal wall. It is a fact worthy of notice 

 in this connection that in many, indeed nearly all, species having both hydrocladial septal ridges 

 and posterior intrathecal ridg3s the latter are situated immediately in front of the former and 

 appear to be identical in structure. However this may be, it seems simplest and best to consider 

 both the anterior and posterior ridges as intrathecal ridges, as does Bale, rather than to make 

 a distinction and confine the term to the latter, as does Allmaii. 1 Xone of the American species 

 of the Eleutheroplea have a recognizable intrathecal ridge, with the exception of 7'. jilianilix 

 Kirchenpauer (fig. 18), where it is present in a rudimentary form (Bale). In the Statoplea, 

 however, it is usually present in some form or othef, the exception being Aglauphenia crenata, 

 Cladocarpus flexuosus, C. dolichotheca, Thecocurpita bispinosus, and Thecocarpus distmin. 



The ridge is posterior in all American species of Aglnophenia, which undoubtedly belong to 

 that genus; in all species of Tliecocririiim and Cladocarpus that I have examined which have any 

 intrathecal ridge at all; in Aglaophenopsis, except A. distamn ; and in Lytocarpus, except L.philip- 

 pinus, where it is rudimentary. 



There are a few American species in which the ridge is anterior, as in Chtd<n'rpus carintttus 

 (tig. :'<(>), Lytocarpus pkilippinus, and the American species of Jlttlitionairiu (Plate XXXIII, tig. 8). 

 In the first two of these there is also a posterior ridge. Bale remarks that an opposite condition of 

 affairs prevails among the Australian Plunmlarid;e, where the ridge is usually anterior and only 

 exceptionally posterior. The ridge varies from a mere rudiment to a strong anterior shelf which 

 completely encircles the hydrothecal cavity, as in Agluophenia miniita (Plate XXI, fig. 1), or 

 extends forward and upward clear across the hydrotheca in an oblique direction, as in A. 

 gnicillima (tig. 22). In no case that I have examined does the ridge extend forward and down- 

 ward. In some species, for example Clitflocarpun neptatnn (tig. 20), the ridge forms a single 

 posterior shelf which ends in much more attenuated laterally projecting prolongations, forming 

 an angle with the shelf. The anterior ridge in Haliconutria (lig. 34) is usually very strong, 

 ending in a knoblike termination as viewed from the side. The anterior wall of the hydrotheca 

 often contains an aperture, through which sarcodal processes from the sarcostyles penetrate into 

 the hydrotheca'. This is particularly apt to be the case where the mesial nematophore has two 

 openings. 



Nemntophorcs. The name nematophore was first applied by Busk'-' to the entire structure 

 which Hincks differentiated into two parts, sarcotheca and sarcostyle, the former designation being 

 applied to the so-called sarcodal processes, and the latter to the chitinotis receptacle into which 

 they retract. As I have already suggested," the more precise terminology would be to apply the 

 name nematophore to the latter structure and use the words sarcostyle and sarcotheca as proposed 

 by Hincks. The word nematophore has, however, become so fixed in the literature of the subject, 

 especially in systematic works, as applied to the chitinous receptacle without reference to its con- 

 tents, that it seems wise, on further consideration, to use but the two terms "nematophore'' 

 applied to the sarcotheca without necessary reference to its contents, and "sarcostyle" as applied 

 to the "defensive zooid,'' "machopolyp," "protoplasmic process," "sarcodal process," etc., of 

 various writers. Whether the term is an apt one or not is aside from the question now that it has 

 become firmly intrenched in continuous use. 



Nematophores have been divided by Allman into four classes, according to the position they 

 occupy in the colony." Nematophores found in pairs at the side of, or immediately above the hydro- 

 theca3 are swp >''"'" '.'/'''"'' nematophores; those found on the front of the hydrocladia, mesial i/cmat<>- 

 plwren; those on the main stem or branches are caitline nematophores; and dually, those attached to 

 the gouangia or special protective branches of the gouosome are gonoxomal nematophores. They 



1 Report on the Hydroida dredged by H. M. S. riiull'inji-r during the years 1873-76, Pt. 1, Pliiuiiilaritl;i-, 1HSU, p. .">. 



- Huuteriau Lectures, manuscript, London, 1854. 



3 Journal of the Marine Biological Association of tin- United Kingdom, New Ser., IV, Xo. -, 18!Mi, p. ll'J. 



