COMPLEMENTAL MALE. 207 



Affinities. — This species most closely resembles I. 

 Cumingii, and cannot be distinguished externally, except 

 by the absence of the blue colour on the marginal and 

 interior portions of the valves ; and this can hardly be 

 ascertained without separating and cleaning them, owing 

 to the blueness of the underlying corium. Internally 

 some slight differences may be perceived in the form of 

 the valves. Considering these so slight differences, it is 

 highly remarkable that this species should be hermaphro- 

 dite, whilst J. Cumingii is unisexual. There is a greater, 

 though still slight, difference in the included animal's 

 body ; the palpi in L quadrivalvis are blunter, the man- 

 dibles smoother, the olfactory orifices darker-coloured ; 

 the rami of the first cirrus more unequal, the spines 

 more numerous on the segments of the posterior cirri, and 

 lastly and most conspicuously, the caudal appendages 

 are very much longer relatively to the length of the sixth 

 cirrus, than in Ibla Cumingii. 



COMPLEMENTAL MALE. 



I have examined one specimen of the hermaphrodite 

 /. quadrivalvis, preserved in spirits from Kangaroo Island, 

 and one dry from Adelaide, both places in South Australia, 

 and four from an unknown locality, purchased from 

 Mr. Sowerby ; and within five out of these six specimens, 

 males were attached. In one of them, two males of dif- 

 ferent ages were included, one adhering to the peduncle 

 of the other : in I. Cumingii, also, it may be remem- 

 bered, there was a case of two males parasitic on one 

 female. I may add that I opened another quite young 

 specimen, from Adelaide, not counted with the above, and 

 it was without a male. The males in the five specimens 

 were attached low down, at the rostral end, almost in a 

 horizontal position, stretching across the bottom of the 

 sack ; one of them, however, was placed considerably on 

 one side. One individual which I measured, was ^ths of 

 an inch in length, and —ths in width in the widest part, 



