REPORT ON THE THNICATA. 
07 
The single specimen for which this species is formed was dredged in Tangier Bay on 
the Coast of Morocco, during the cruise of H. M. S. “ Porcupine ” in the summer of 1870. 
It is a small colony of irregular shape attached by a narrow base, to which sand, &c., is 
adhering (PI. IV. fig. 6). 
From the massive form of the specimen and the considerable thickness of the test 
there can be no doubt that it belongs to the genus Pohjcijcliis, and it differs in many 
respects from the last described species and from all other known species of Polycyclus. 
It is closely allied in some respects to Polycyclus lamarchi, and I was at first inclined 
to regard it as being merely a variety of that species, but a detailed examination revealed 
so many points of difference that I believe it is best to describe it as a distinct though 
closely allied species. 
The general colour is pale yellow or yeUowish-grey. The ends of the Ascidio- 
zooids next the common cloacal apertures are each marked by a short brownish- 
purple streak, which, as it is traced towards the branchial aperture, dies away in 
the middle line but is continued a little further anteriorly at the edges. The 
body of the Ascidiozooid is rather more opaque than the surrounding test, Imt of 
much the same yellowish colour. The base of the colony, where test only is present, 
is of a darker but more transparent grey with opaque white dots thickly scattered 
over it. 
The systems are not very numerous, and are not nearly so closely placed as in the 
last species. They are always distinctly separated from one another (PI. IV. fig. 6). 
The systems are all nearly circular in form, and contain about six to eight Ascidiozooids 
each. The part of the Ascidiozooid seen on the surface is of elongated ovate form, with 
the narrower end pointing towards the centre of the system. The largest ones measure 
about 2'5 mm. in length and 1'5 mm. in greatest breJtdth. 
Under a low power of the microscope the small branchial aperture, surrounded by a 
rather large opaque white sphincter, can be seen. The endostyle and the peripharyngeal 
band are also visible, and there are two opaque white spots placed one in the middle of 
each side between the sphincter and. the peripharyngeal band. The nerve ganglion is also 
visible, and in many of the Ascidiozooids the anterior part of the branchial sac can be 
made out, the outlines of some of the stigmata and the upper ends of the six internal 
longitudinal bars being seen. In one or two cases the tentacles are also distinguishable. 
In this species, as in Botrylloides purpureum, a much greater amount of the internal 
anatomy is visible from the surface than is usually the case. This is due mainly to the 
great transparency of the superficial layer of the test and the absence of pigment in the 
mantle. 
The common cloacal apertures can be readily seen with the naked eye in most of the 
systems. They are nearly circular, and have projecting membranous margins. Under 
a slight magnification this margin is seen to be lobed, one lobe usually corresponding 
