298 Mr. H. J. Carter on new Species of 
XXXIV.—On new Species of Hydractiniide, Recent and 
fossil, and on the Identity in Structure of Millepora alcicor- 
nis with Stromatopora. By H. J. Carrer, F.R.S. &e. 
[Plate XVII. ] 
In the ‘ Annals’ for 1873 (vol. xi. p.10) I have inserted a 
description of a branched chitinous polypary, to which the late 
Dr. J. E. Gray had given the name of Dehitella atrorubens, 
under the idea that it was a sponge, but which subsequently 
proved to be a species of Hydractinia; and I have now to 
present the following description of a chitinous polypary like 
that of Hydractinia echinata, but with short branches here 
and there similar in form and colour to those of Dehitella 
atrorubens, which, on the contrary, grows into a bush-like 
polypary from a single, smooth, compressed, root-like stem. 
Hydractinia arborescens, nu. sp. (Pl. XVII. figs. 1-4.) 
Polypary chitinous. Laminiform, surmounted by spines 
and branches indiscriminately scattered over the surface. 
Colour dark amber-brown (Pl. XVII. fig. 1). Surface follow- 
ing the form of the object over which the polypary may be 
growing (in this instance a turreted shell like Phos senti- 
cosus, family Buccinide) ; uniformly even, except where in- 
terrupted by the presence of spines and branches; presenting 
a granulated reticulation of short, broken, raised, serrulated 
ridges more or less surrounding minute holes once occupied 
by the polypites and other soft parts of the ccenosare (figs. 2, 
b, c, and 3, a, 6); traversed throughout by a venation of 
anastomosing grooves whose depth and distinctness is in pro- 
portion to their size, the largest being 1-180th inch in dia- 
meter (fig. 2, a, and fig. 4). Holes of the polypites, which are 
very numerous and equally present along the course of the 
vein-like grooves, as in the interstices of the granulated reticu- 
lation, may be best seen where the ccenosare has been well 
washed out, varying in size, according to their office, from 2 
to 3-1800ths inch in diameter (fig. 2). Spines conical, vari- 
able in size and length, scattered more or less partially over 
the surface so as to leave here and there plane intervals of 
greater or less extent; often growing into erect branches 
variable also in length and thickness (fig. 1, aaa), the 
largest, which in this instance forms one of a group at the 
anterior extremity of the shell, being 1-12th inch in dia- 
meter at the base (fig. 1,6), and the remaining longest portion 
of the rest (for they have all been broken off more or less close 
to their origin in the laminiform part of the polypary) 1-3rd 
