79 



rocky headland about seventy miles south of Port Jackson, near 

 Jervis Bay. 



2. — Trigonia margaritacea, Lk. 



This species was in all probability also obtained by Pe'ron during 

 the same voyage, the more so as it, too, has received its specific name 

 from Lamarck. The shell, although at first sight a very similar one to 

 the preceding, when examined carefully has many essential differences. 

 It is a much coarser shell, more decidedly trigonal in shape, the ribs are 

 not nearly so closely set with the comb-like projections, and the spaces 

 between the ribs are more finely but less regularly striated, the striations 

 not apparently extending so high up the face of the shell. The epider- 

 mis of T. margaritacea is also always of a much darker colour and of a 

 coarser nature than that of T.pectimta, while the pearly interior is persis- 

 tently of a deep purple hue. To this last characteristic it no doubt owes its 

 name. Thisisoneof the species to which I referred as having been found by 

 myself at its known most western limits on the south coast of Australia 

 Hitherto it had only been taken in Bass's Straits, off the coast of Tas- 

 mania. It seems to have been unknown to Mr. G. F. Angas as a South 

 Australian shell when he published his list of South Australian Bivalves 

 in the Proceedings of the Zoological Society of November, 1865, and it 

 must have been about that time when I obtained it on the eastern shores 

 of St. Vincent's Gulf, on the long stretch of sandy beach between Glenelg 

 and the Semaphore. Since then it has been found by other collectors at 

 the same place, and further south at Aldinga, but always in a more or 

 less worn condition. Its particular habitats in our waters have not yet 

 been discovered, no live specimens having yet been dredged. Of the four 

 worn valves shown by me only one is in a sufficiently good state of pre- 

 servation to exhibit the colour of the nacreous interior, but the general 

 contour of the shell and the bifurcated appearance of the process which 

 partially emarginates the anterior muscular impression in the left valve 

 are distinctive characters enough to show that it is a true T. margari- 

 tacea, and not a new species. T. margaritacea is catalogued by me in 

 my list of South Australian Shells published (for private circulation only) 

 in 1875. 



3. — Trigonia nobilis — A. Adams. 



This species is unknown to me, and I would hazard an opinion, 

 although somewhat presumptuous on my part, that may only be a very fine 

 example of either of the two foregoing species. 



