24 THE AUSTRALIAN MUSEUM. 



Tentacles 16, 8 larger and about 8 smaller, placed alternately. The 

 larger ones much branched. 



Dorsal tubercle formed of 2 spiral cones turned away from each other. 

 Gonculs a large single mass upon each side. 

 Locality. Port Jackson, about 20 specimens. 



This is a small Microcosmus, but apparently, from the condition of the 

 gonads, quite mature. It has the usual crumpled condition of the test, 

 characteristic of the genus. Although the apertures are on considerable 

 prominences (PI. Cyn. V., figs. 1 3), the actual cross-slit openings are 

 very minute. The figure (fig. 1) is not an exact portrait of any one of 

 the specimens, but is a combination drawing presenting what seem to me 

 the average characters. Each specimen seems more or less contracted 

 or abnormal in some part. In a group like Ascidians, where there may 

 be so much individual variation externally, due merely to an accident of 

 the environment, I believe it would generally be more useful, where there 

 are a number of specimens of a new species, to prepare a combination 

 figure, giving what the observer considers the permanent characteristic 

 features, rather than an exact representation of one individual with all its 

 defects. Figure 3 shows a variation in form, and fig. 2 a cluster of 

 half-a dozen specimens adhering together. 



The sizes of the 4 best specimens are as follows : 



A. 3'5 cm. X 3 cm. x 2 cm. 



B. 4 ,, x 25 ,, x 1-5 ,, 



C. 3 x 2 x 2 



D. 3 ,, x 2-5 ,, x 1-5 ,, 



The mantle is about equally muscular all over. 



The branchial sac is neat and regular in its vessels. In most cases 

 it has 10 folds on each side. The internal longitudinal bars are rather 

 narrow (fig. 5), and between the folds they are not placed at very regular 

 distances apart. In some places the transverse vessels are arranged as 

 follows : very broad, narrow, narrow, narrow, broad, narrow, narrow, 

 narrow, very broad (see fig. 6) ; in other places they are less regular. 



The prolongation of the test which lines the branchial siphon (see 

 fig. 4 sc.) bears in its outer narrower part a large number of minute spines 

 or pointed scales, so close set as to produce a shagreen-like surface. 

 This condition I first of all pointed out in 1882, in the case of Cynthia 

 arenosa. Later on (1884) Lacaze-Duthiers described it in some other 

 Cynthiidae, and in 1885 I discussed the matter in a note on the armature 

 of tho branchial siphon. Next comes a much corrugated zone, which 

 marks the position of the sphincter muscle (fig. 4, cor.). Further down 



