CATALOGUE OF TUNIC ATA. 81 



This species and the last described are undoubtedly very closely 

 related ; if, indeed, they are distinct. They differ chiefly in their 

 tentacles and the dorsal languets, and these may possibly, when more 

 specimens come to be examined, be found to vary considerably. In 

 the meantime, I think it best to describe both forms fully, even though 

 it may afterwards become necessary to unite them under one specific 

 name. 



Polyclinum complanatum, n. sp., PI. Pel. I., figs. 912. 



External appearance. The colony is very wide and flat, but has 

 evidently, in the only specimen, been very much distorted by pressure 

 from above downwards. The peduncle has been pressed up against the 

 Ascidiarium, and its wide base of attachment is now concave (PI. Pel. I., 

 fig. 9). The Ascidiarium is almost rectangular in outline, and is of a 

 yellowish white colour. The peduncle is rather greyer, and is slightly 

 encrusted with sand. The dimensions are as follows : Length of 

 Ascidiarium 3 - 5 cm., breadth 10 cm., thickness 8 cm. Length of 

 peduncle 2 cm., thickness 4 cm. 



The Ascidiozooids are from 7 to 15 mm. in length, and are 1'5 mm. in 

 breadth. They lie principally near the base of the Ascidiarium, but are 

 not much retracted from the surface, the two apertures being very 

 distinctly visible. The body consists of thorax, abdomen, and a short 

 post-abdomen, with vascular appendage (fig. 10). The abdomen is 

 twice or more the length of the thorax. The vascular appendages are 

 branched. Incubatory pouches crowded with embryos may be present. 



The test contains numerous large spherical, stellate, and fusiform test 

 cells. 



The mantle has longitudinal muscle bands, which run over the thorax 

 and bifurcate near the branchial siphon, each half then joining with the 

 neighbouring half under the sphincter muscle. 



The branchial sac is very opaque, and is corrugated on account of the 

 contraction of the mantle over it. The stigmata are very long, about eight 

 or nine times their width (fig. 11). The inter-stigmatic vessels are narrow. 



The dorsal lamina is represented by a series of slender languets, 

 which may be coiled (fig. 12), and are set rather less than their own 

 length apart. 



The tentacles are about 12 in number, and all of one size. 



The alimentary canal consists of a long oesophagus, a simple and wide 

 stomach, and a thin-walled intestine, which only reaches a little way up 

 the thorax (fig. 10). It is usually distended with faecal pellets. 



