8 
URNATELLA GRACILIS, A FRESH-WATER POLYZOAN. 
as iu more mature specimens, it may become involute, as represented in figure 1 
J ItlLL 1. 1 • 1 1 1 
'I'he segments of the stem of Urnatella are chiefly urn-like in sliape and are nearly 
uniform in size and other respects, except tire first one and the last two of the series 
next tlie bell. The body of tlie urns forms the swollen, translucent, light-colored 
portions of the segments,' and exhibits a more or less finely and transversely wrinkled 
appearance, lined with brown in the same direction, and also spotted with bronn, or 
often furnished with little tubercles of the same color. The neck and pedicels of the 
urns conjoin one another in the different segments, and are black and opaque. The first 
segment of the stem is likewise urn shaped, like those which usually .succeed it, but is 
considerably larger, and its pedicel expands into a broad, circular or oval disk, which 
tightly adheres to the stone on which tlie polyp is attached. Tlie two segnumts of the 
stem of Urnatella, next the bell, are narrower, more cyiindroid, softer, more translucent 
and more flexible than the others, and they are not abruptly contracted and blackened at 
the extremities. The last segment, attached to the bell, is cylindrical or often clavate, 
and colorless. The jireceding .segment is barrel-shaped, or intermediate in shape to 
the former and the urns, and is colorless or slightly colored like the latter. 
The ])olyp-stem of Urnatella is composed of an external homogeneous, tougli, 
chitinous integument, transparent and colorless, or of a pale amber hue, except at the 
constricted portions of the stem, where it appears black, and elsewhere, where it 
api)ears lined and dotted with brown. It extends in a delicate layer uijon the terminal 
.segments of the stem to the outside of the polyp-bell. The disk of attachment of th(‘ 
polyp-stems is mainly composed of an extension of the chitinous integunu-nt. 
Within the more translucent portions of the .stems of Urnatella, a cylindrical cord 
is seen extended throughout the axis, from the base of attachment to the polyp-hell. 
It fills the narrower imrtions of the urn-like segments, and usually also the whole 
of the .segment next the bell. In the wider portions of the stem a more transhicent 
interval is occupied by indistinct and undetermined material. The axis cord of the 
stem is superfic-ially finely striated in the length, and interiorly appears to be composed 
of a granulated substance, as represented in figure 2, Plate I, where a portion is seen 
extending from the end of the first segment of a stem. 
Projecting usually from the opposite sides of the urn-like .segments of the stem of 
bud'b., 171.7"°"' I ”i8i»nlly look,..! „p„n 
matUT 1.1 P'O'i-g tl,e„. be e,.,p,y shell, of el.itin,,,., 
el,e,vl,e,e. sleti.ne, a 1 eatabl.si.ed ... the fon.,.lati„„ of ,-,>l„„ie, 
and p,rely t,v„ 1 °°°“" °"‘»' 
I apinar on „pix„.te side, of the san.e segment. Oeeasionallv 
