Ill 



NOTE ON A VERY LARGE SPECIMEN OF HIPFOPUS HIFPOFUS 

 AND ON LARGE SPECIMENS OF TRIBAONA GIGAS. 



By Edgar A. Smith, F.Z.S., etc. 



Read loth May, 1898. 



Wha.t may be regarded as full-grown specimens of this species usually 

 average from 6 to 9 inches in length, and the largest hitherto recorded 

 measured 10 inches. Iviister,' in his Monograph of this genus, gives 

 61" inches as the length, whilst the Rev. J. E. Tenison- Woods "■ 

 observed a specimen upon the reefs at Port Douglas, N.E. Australia, 

 which was 10 inches long. The largest example in the British 

 Museum is 9f inches in length, 19 in circumference, and weighs 

 4 lbs. 5 ozs., whereas a specimen recently acquired from the 

 Philippine Islands is I3|^ inches long, 30 round, and 16 lbs. 9 ozs. 

 in weight.^ Although only 3| inches longer than our largest 

 specimen, the difference which is indicated by the contrast in the 

 weight is very conspicuous. The shell itself does not differ materially 

 from ordinary specimens, but is somewhat pointed and produced 

 posteriorly, so that the position of the umbones is relatively less 

 central, being 4^ inches from the anterior extremity of the shell, that 

 is, only -g- inch more remote than in the 9f inch specimen. They are 

 also unusually incurved, so that the tips are fully an inch from 

 the hinge-line, whereas in ordinary specimens they almost touch it. 

 Another feature noticeable is the shallower grooves within the valves 

 that correspond to the external ribs, and the moi'e feeble sulcation of 

 the intervening spaces. The specimen is much incrusted with various 

 marine growths, and more or less worm-eaten and water-worn, but the 

 characteristic pui-ple-red spotting is observable near the umbones. 



Although quite small in comparison with the so-called Tridacna 

 gigas, the present specimen, with the exception of some of the Pinnas, 

 probably ranks next in size among living bivalves. A few examples 

 of Ostrea and vEtheria may be longer, but then they are narrow 

 and lighter. 



' Conch. Cab., 1868, Monog. Tridacna and Hippopns, j3. 8. 



2 Proc. Linn. Soc. N.S. Wales, 1880, vol. v, pp. 124-5. 



^ Messrs. Sowerby & Fulton have another specimen II5 inches long. 



VOL. III. DECEMBER, 1898. 8 



