98 The Genera of the Plmnulariidce, 



the hydrotheca usually has two deep, narrow sinuses, with 

 a long, narrow tooth between them^ but they are sometimes 

 comparatively shallow. The back of the hydrotheca can 

 only be properly seen in front view when the hydrotheca 

 is tilted forward. There is a deep inflection below the 

 recurved aperture^ not consolidated into an intrathecal ridge, 

 but projecting so far into the hydrotheca that it is con- 

 spicuous in a front view, its inner margin having a bidentate 

 form at the centre. 



Aglaophenia IIuxleyi, Busk 



In this species the hydrocladia are replaced at the distal 

 ends of the branches by hollow spines without hydrothecse, 

 as first pointed out by Professor Allman, who has made the 

 species the type of his new genus Acanthocladium. The 

 figure of the hydrothecse in the '' Challenger" Report is 

 erroneous in several particulars, noticeably in representing 

 the margin as entire, while in reality it has a broad, 

 rounded sinus at the back; in omitting the anterior tooth, 

 which, though not large, is distinct and characteristic; and 

 in showing the anterior sarcotheca as a long slender spine, 

 closed throughout, whereas its true form is, in lateral view, 

 remarkably beak-like, very stout where it joins the hydro- 

 theca, and tapering rapidly upwards, with the point 

 expanded laterally, while it is open on the distal side from: 

 base to summit. All these features are correctly character- 

 ised in Mr. Busk's original description, except that the open 

 condition of the sarcotheca is not mentioned. This, however, 

 is not apparent in an ordinary view, but on looking down 

 on the hydrotheca from above it is easy to trace the opening 

 down the sarcotheca, and to perceive that one of the- 

 margins overlaps the opposite one near the top. The 

 expanded summit is usually, but not always, finely crenate. 

 The crenations of the hydrotheca margin are much more 

 pronounced in the " Challenger" figure than in any of the 

 specimens which I have met with. The anterior intrathecal 

 ridge attains its fullest development in this species, starting- 

 from the base of the mesial sarcotheca and projecting down- 

 ward more than half-way through the hydrotheca, which it 

 divides into two chambers. The posterior ridge is quite 

 rudimentary. 



Professor Allman has figured the corbula of this species,, 

 the ribs of which are curved filiform processes, armed with 



