THE WELL-BORING AT RICHMOND, SURREY. 779 
| yet traces of the spicular composition of the fibres were recognizable 
in all, though not always sufficiently clear to allow of their being 
figured. 
Order CALCISPONGLA. 
Family PHaRErRones. 
Iyoporra micvLA, Hinde, n.sp. Plate XXXV. figs. 1, 1 a—d. 
Sponges small, apparently free, round or irregular in outline; 
varying from 2:5 to 10 millim. in diameter. The outer surface 
presents, as a rule, only the smooth naked fibres, which are arranged 
so as to leave interspaces of an irregular form. In some examples 
the base and a portion of the lateral surface show traces of a smooth 
dermal layer. There are no indications of distinct canals, so that 
the circulation must have been wholly carried on in the interspaces 
between the fibres. 
The fibres are of a somewhat coarse character ; measured in a 
thin section, they vary from -14 to °25 millim. in thickness. They 
are composed of relatively large, three- and perhaps four-rayed 
spicules in the central and subcentral portions, with filiform slender 
spicules bordering the exterior of the fibre. The complete form of 
these border spicules cannot definitely be ascertained ; in one instance 
the spicule appears to possess three rays, but it is possible that 
uniaxial forms may be present as well. The rays ofthe large axial 
spicules reach a length of -29 millim. by ‘05 millim. in thickness. 
The dermal layer is compact in character and apparently composed 
of three-rayed spicules of various dimensions; the rays of these 
spicules overlap each other in anirregular manner. In one specimen 
the spicular rays are sufficiently clear to permit of measurement, and 
the largest seen is ‘21 millim. in length, thus corresponding in size 
to the axial spicules of the fibre itself. 
The examples of this species are by far the most numerous of any 
met with in the boring. They are very fragmentary in appearance, 
but the outer dermal layer shows that some of them at least are 
entire sponges. On the outer surface of the specimens the fibres 
are clearly shown free from matrix, but in thin sections they are 
see to be imbedded in a matrix of clear granular calcite, in which 
they appear as labyrinthic bands of a cloudy aspect. In these 
bands more or less clearly defined lines indicate the outlines of the 
spicules in the fibre; but it is rare to find even an entire spicular 
ray in theplane of the section. Portions of two and, more rarely, of 
the three rays can be detected; but in no instance can more than 
three rays be seen, though it is quite possible that some of these 
spicules may have possessed a fourth ray at right angles to the other 
three. The condition of the specimens also prevents any accurate 
determination of the proportionate length of the spicular rays; but 
the transverse sections are circular. The rays may be either straight 
or curved, and they taper in some instances very gradually, in others 
rapidly, from the central junction of the spicules to the acute 
extremity. The form of the smaller filiform spicules in which the 
