8 Memoirs of the Indian Museum. [Vor. VI, 
Hexacrobylus indicus, Oka. 
(Pl T, fig. 3; pl. II, ses. 8-13; pl. III, fies 73202) 
Hexacrobylus indicus, Oka, A., Zur Kenntnis der zwei aberranten Ascidiengattungen, Dicopia, 
Sluiter und Hexacrobylus, Sluiter. Zool. Anz. Bd XLIII, No. I, 1913. 
External Appearance.—The body is ovate in shape, and is slightly compressed 
laterally (Pl. I, fig. 3, and pl. II, fig. 8). The anterior or upper end is broad and 
rounded, the posterior or lower is somewhat narrower and slightly pointed. The 
dorsal and ventral edges are equally convex. The branchial aperture is situated a 
little above the middle of the ventral edge, and is very large and conspicuous. The 
atrial aperture is placed in the middle of the anterior surface, 7.e.at the summit of 
the body, looking anteriorly; it is very small and insignificant. The animal is not 
attached, having its lower end simply imbedded in sand or mud of the bottom. 
The configuration of the branchial aperture is very peculiar. It is a wide trans- 
verse slit, more or less gaping in all the specimens, and guarded by what seems at 
first glance to be thick projecting warty lips. In reality the opening is surrounded 
by six pinnately branched processes arranged in such a manner that two of them 
stand on the anterior border and the remaining four on the posterior border of the 
aperture. They are not all of one size, those on the anterior border being the 
largest, while the median ones on the posterior border are slightly smaller than the 
lateral ones (Pl. II, fig. 9). In consquence of preservation in alcohol they are all 
strongly contracted and bent inwards, and the stem exhibits a series of transverse 
furrows corresponding to the intervals between the lateral branches, of which there 
are five to seven on each side. These branches are again ramified (Pl. II, figs. 10 _ 
and 11). Judging from the development of muscular fibres in their interior it is 
highly probable that these processes could be expanded during life, like the tentacles 
of Alcyonarians, to serve as an organ for collecting food. 
The external surface is covered all over with delicate woolly hairs. These gener- 
ally are rather short, but at the lower end of the body, which seems to have been 
buried in mud or sand, they are much longer. Sand grains and foraminiferan shells 
are seen here and there adhering to these hairs. The colour of the animal is a light 
brownish-grey, owing to fine mud particles on the outer surface. Held against the 
light, the body is found to be semi-transparent. The six tentacle-like processes 
of the branchial aperture are almost destitute of hairs and are much darker. 
The dimensions of the five specimens are as follows:— 
Specimen. Length (antero-posterior). | Breadth (dorso-ventral). Thickness. 
No. I 34 mm. 23 mm. 20 mm. 
No. 2 28 min. 20 mm. 15 mm. 
No. 3 25 mm. 18 mm. 14 mm. 
No. 4 20 mm. 15 mm. Io mm. 
No. 5 Ig mm. 15 mm. I2 mm. 
The Test is composed of two layers, an outer and an inner. The outer layer, 
which is formed mainly of the basal parts of the delicate hair-like processes, is very 
