18 THE AUSTRALIAN MUSEUM. 



transverse vessels, which stands on a plane internal to the inter-stigmatic 

 vessels, which are much finer. These larger internal vessels contain 

 spicules. 



Dorsal lamina very slight, dying away almost at once behind the 

 dorsal tubercle. 



Tentacles 24 in number, 12 large and 12 small, placed alternately. 



Dorsal tubercle forming two close spirals with their apices directed 

 away from one another. 



Locality. Port Jackson, about a dozen specimens. 



This species differs from the other Boltenias externally in its knobbed 

 appearance (PI. Cyn. II., figs. 1, 6, and 7), and internally in the 

 structure of the branchial sac, the number of the tentacles, and the 

 nature of the dorsal tubercle. Many of the specimens are covered with 

 a smooth closely incrusting layer of sponge. This is one of the largest 

 of Simple Ascidians. Although the stalk is not so long, the body attains 

 a larger size than in Boltenia pacliydermatina. 



The sizes of the specimens before me are as follows : 



No. Body. Stalk. 



1 ... 45x2x1 cm. ... 12-5 cm. 



2 ... 4 x 2 x 1 ... 8 



3 ... 5 x 1-5 x 1 13 ,, 



4 ... 6-5x3x2 ,, ... 20 



5 ... 4'5 x 1 x 2 ... 4 ,, 



6 ... 9x5x3,, ... 14 ,, 



7 ... 6-5x3x3 ... 7 



8 ... 5 x 1-5 x 1-5 ,, ... 9 ,, 



9 ... 4 x 1-5 x 1 ... 7-5 



10 ... 7-5 x 4 x 2-5 ... 20 



11 ... 5-5 x 3 x 2-5 ... 25 



12 ... 12 x 7 x 5 ,, ... cut short 



which shows a considerable variation in the proportions. The amount of 

 tuberculation also differs in specimens. There may be as many as 

 40 knobs on the body. The apertures are very remarkable. In one 

 specimen I can count 13 lobes round the branchial aperture and 12 

 round the atrial, but others differ; frequently, however, four of the 

 lobes are much larger than the rest, so as to present a 4-lobed 

 appearance (see figs. 2 and 3). 



The branchial sac is very strong. There are some wide irregular 

 vessels on the back, then the fine inter-stigmatic network, and then 



