380 DR. H. L. JAMBSOI^ ON I'HE [^V^' 1^' 



Section lb. TeetJi very rudimentary. Shell fiat as in M. margariti- 

 fera. Posterior marginal notch absent or slightly developed. 

 Eostrum not sharply marked off from, the inner surface of the 

 valve. Longest dorso-ventral axis perpendicidar to the hinge- 

 line. 

 Species 4. Mabgabiti]?eea sugillata. 



Avicula sugillata, Eeeve, 1857, no, 27; Cape Hillsborough. 

 Type B.M. 



Avicula fimhriata, Eeeve (nee Dunker), 1857, no. 25 ; N.W. 

 Australia (nom. prceocc). Type B.M. 



Avicula {Meleagrina) reeviana, Dunker, 1872, p. 45, tab. 15. 

 fig. 1 (after Eeeve), for A. fimbriata, Eeeve. 



Avicula irradians, Eeeve, 1857, sp. 35 ; Australia. Type B.M. 



The types of Eeeve's three species are all very young shells. 

 There are a few older examples in the Museum, acquired since 

 the date of Eeeve's monograph. I also possess a series of this 

 shell, which I collected in Torres Straits. The complete inter- 

 gradation between Eeeve's three species makes it quite impossible 

 to regard them as distinct. 



I regard M. sugillata as the Torres Straits representative of the 

 " Sharks Bay shell " of the London markets. The latter I am 

 describing under a distinct name, as a well-marked geographical 

 race, even if not actually specifically distinct. 



The form of the adult M. sugillata is very variable, approxi- 

 mating to that of the Sharks Bay shell, but as a rule more convex, 

 and with a shorter hinge relatively to the size of the valves. The 

 colour is a dirty greyish yellow, with four or five brownish radial 

 bands, which may be indistinct and imperfect, or may fuse to 

 give the shell a uniform dark colour. 



The lappet-like processes of the lip are large (especially in 

 young examples), delicate, and characteristically "crimped" so as 

 to be more or less 'l/'-shaped in section, a feature easily discernible 

 in Eeeve's figures. The lappets are so thin as to be usually 

 broken ofi^ except just at the lip ; but here they are generally 

 crowded together in grown shells, giving the lip a curious thickened 

 appearance, "which I have elsewhere seen only in specimens of 

 M. margaritifera grown in unsuitable, silt-laden water. 



The inside of the lip is dirty yellow, with cloudy brown markings, 

 corresponding to the dark radial bands. These markings show a 

 strong tendency to fuse and form a dark zone on the inner edge 

 of the lip, next to the nacre. The nacre is white, with yellowish 

 or greenish tints, but somewhat lacking in lustre. 



Cape Hillsborough, N.W. Australia (Reeve). Port Essington 

 and Torres Straits (spp. in Museum). Prince of Wales Island and 

 Thursday Island, Torres Straits {H. Lyster Jameson). 



This species, although closely resembling the Sharks Bay shell, 

 has not yet found its way into the markets. 



