42 AGLAOPHENTA GRACILIS. 
intrathecal ridge transverse. Supracalycine nematophores stout, slightly 
overtopping the hydrotheca; mesial nematophore attainmg nearly half 
the height of the hydrotheca, adnate for nearly its entire length; two 
cauline nematophores on each internode of stem, one of which is situated 
close to the axil of the pinna, and the other near the distal end of 
the internode. 
Gonosome. — Corbula with about ten pairs of leaflets; leaflets quite free, 
narrow, with denticles nearly equally developed on each edge and with 
a spur-like denticle at its base; peduncle of corbula carrying a single 
hydrotheca. 
Off Sand Key, from a depth of 100 fathoms. 
In its trophosome this species comes very near to Aglaophema lophocarpa. 
It differs from it, however, in the occurrence of a slight angular bend be- 
tween every two internodes of the pinne, and more especially by its open 
corbule. 
There can be little doubt that the open condition of the corbulx is 
not here the result of an immature state of these bodies. Like a similar 
condition of the corbule of other species, it is of considerable morpho- 
logical interest as a persistent state of a condition elsewhere transitory. 
The nature of the denticles along the edges of the leaflets is very 
obvious in this species. They are plainly seen to be nematophores of 
the ordinary Aglaophenian type. Their cavity communicates by an aper- 
ture in the base with the interior of the leaflet, and through this 
aperture their contents become united with the ccenosare of the leaflet. 
The ccenosare does not uniformly fill the leaflet, but is disposed in the 
form of a loose, irregular network of intercommunicating channels. 
Aglaophenia gracilis. 
Pl. XXV. Figs. 1-4. 
Trophosome.— Hydrocaulus attaining a height of about three inches, 
sparingly branched, not fascicled; pinne alternate, springing from a point 
near the distal end of each internode; internodes of pinne with two 
strong but short septal ridges, one on a level with the short, strong 
intrathecal ridge, the other on a level with the base of the supracaly- 
cine nematophore. Hydrothece deep, slightly widening towards the 
orifice, with strongly toothed margin; intrathecal ridge strong and short, 
