PEARLS AND PEARL-OYSTERS. 209 



of this plan, additional instalments for the Shark's Bay grounds have, as a matter of 

 fact, been recently transported to the Dirk Hartog cultivation grounds, under the able 

 management of Mr. John Brockman, the Shark's Bay Pearl Shell Fishery inspector. 



Some attention may now be given to that second and smaller species of 

 Mother-of-Pearl shell which is indigenous to Shark's Bay and which in former years 

 constituted a by no means unimportant fishery. This is the Meleagrina imbricata of 

 conchologists, known to the trade as Shark's Bay shell, since, though occurring in more 

 or less abundance throughout almost the entire northern moiety of the Australian 

 coast-line, it is only in Shark's Bay, Western Australia, that it grows in such 

 abundance as to constitute a systematic fishery. Considerable difficulty has been 

 experienced in precisely fixing the technical title of this shell. The above name was 

 originally awarded to it by Eeeve, but he at the same time conferred upon other 

 examples from the Australian Coast, which are evidently young or local variations 

 only of the same species, many additional titles, including notably those of irradians, 

 lacunata and fimbriata, any one of which is also applicable. Meleagrina imbricata, in 

 the British Museum collection, however, representing the type most nearly coincident 

 with the shell's normally matured form, the name has been adopted in these pages. 



The growth habit of this Shark's Bay shell is very distinct from that of the 

 large tropical species. While the latter type usually occurs as solitary individuals, 

 which in their matured condition lie loosely on the reef or sea-bottom, Meleagrina 

 imbricata grows in dense clusters attached to one another or to other objects by 

 a permanently present " byssus," or bundle of thread-like filaments. A similar 

 anchoring byssus is also possessed by Meleagrina margaritifera in its younger and 

 half-grown stages, but is dispensed with on its arriving at maturity. Two characteristic 

 groups of Shark's Bay shell, in the one instance forming a social cluster and in the 

 other growing on the apex of a species of Pinna, another notable byssus-secreting 

 bivalve, are illustrated in Plate XXXVI. This species of Pinna or Razor shell, as 

 it is locally known, with its attached clusters of Pearl shells, often occurs as crowded 

 colonies, which cover acres in extent. Not unfrequently as many as forty or fifty 

 Pearl-oysters are clustered together on a single Pinna shell, so that the number 

 yielded by even a single acre of them is very considerable. In the larger of the two 

 clusters represented in the Plate quoted, the shells are depicted at about two-thirds 

 of their natural size, the two central ones only being matured specimens. This index 

 to their dimensions will suffice to show how small this species is compared with its 



tropical congener, Meleagrina margaritifera. 

 DD 



