74 THE AUSTRALIAN MUSEUM. 



long oesophagus to the dorsal edge of the branchial sac. It is constricted 

 at intervals. 



Reproductive organs. The masses of spermatic vesicles lie on the 

 posterior edge of the abdomen and extend over the intestine. The vas 

 deferens is large and conspicuous. 



Locality. There are half-a-dozen colonies of this species from Port 

 Jackson. 



In Nature for February 6th, 1890, Dr. R. v. Lendenfeld wrote a 

 letter drawing attention to the fact that in the Australian seas there is a 

 crab which attaches a large Ascidian to its back for protective purposes. 

 In the following number of Nature, vol. XLL, p. 344, I had a letter on 

 the subject, from which I quote the following as to the present species of 

 Amaroucium : 



" The Compound Ascidian referred to by Dr. R. v. Lendenfeld in 

 yesterday's Nature (p. 317) is one of the Polyclinidae and probably a new 

 species. It belongs to the genus Atopoyaatcr, and is closely related to 

 A. infonnis (' Challenger' Report, Part II., p. 171). 



" I have before me now five good specimens of the crab and Ascidian 

 (the crab in this case is Dmmia excavata, Haswell) dredged in Port 

 Jackson, and sent to me by the Australian Museum, Sydney ; they 

 measure as follows : 



SPECIMEN CRAB ASCIDIAN 



(greatest diameter) (length breadth height) 



cm. 

 A 4 



-D... ... '>') ... ... 



C 2-5 



D 2-5 



E 2-5 



" In the largest of them the Ascidian seems to be quite twenty times 

 the size of the crab. 



" I notice in these specimens that the last pair of thoracic legs of the 

 crab, which are much larger than the preceding pair, are turned up 

 dorsally, and are so firmly embedded and attached by their sharp claws 

 in the test of the Ascidian, that it is easier to disarticulate them than to 

 loosen their hold." .... 



At that time I thought I could put the species in my "Challenger" 

 genus Atopoyaster, but I now consider that it will be safer to regard it as 

 an Amarouciwn. 



