47 



juvenile chitons and their adult form, a fact I have pointed 

 out in several of my papers. In this case the juvenile method 

 of sculpture is dropped immediately the adult characters begin 

 to appear. 



Lucilina delecta, Thiele(Faun. Sudwest Austr., III., 1911, 

 p. 397). — While I did not myself take a specimen of this shell, 

 through the kindness of Mr. L. Glauert, of the Western Aus- 

 tralian Museum, I have had the opportunity of comparing 

 specimens "obtained on pearl-shell" from Shark Bay with 

 Dr. Thiele's type, which is in the Western Australian 

 Museum, and I find them the same species. As Dr. Thiele 

 does not figure the shell, I include one in the plate accom- 

 panying this paper. 



I am indebted to Mr. Nils. H. J. Odhner for a specimen 

 of the shell collected by Dr. E. Mjoberg, of the Swedish 

 Scientific Expedition, 1910-1913, and identified and recorded 

 in Kun. Sve. Vet. Hand. Band. 52, No. 16, p. 12, as Tonicia 

 truncata, Sow., from Broome. I find this shell agrees with 

 Dr. Thiele's species. I have been unable to see compared 

 specimens of Sowerby's shell or of Reeves' T. picta, now 

 Lucilina shirleyi, Ire., but Pilsbry's drawing of this latter 

 shows decided differences between that and Thiele's shell; 

 on the other hand, Pilsbry's drawing of Sowerby's T. truncata 

 will fit equally the Broome and the Shark Bay shells — in both 

 the girdle encroaches on the valves, which is said not to be 

 the case in T. picta, Reeve. 



For the present I am not able to decide the question as 

 to whether Dr. Thiele's L. delecta is the same as Sowerby's 

 T. truncata, or whether the identification of the shell obtained 

 by Dr. Mjoberg, at Broome, as such, is incorrect; it is quite 

 certain that one or the other name must be withdrawn from 

 our Australian list. 



Rhyssoplax geraldtonensis, n. sp. 



Two specimens, one adult and the other juvenile, were 

 obtained on the reef, Back Beach, Geraldton, November 7, 

 1920. 



General appearance. — Shell strongly carinated, side 

 slopes steep, slightly rounded, lateral areas much raised and 

 bi-ribbed, pleural areas longitudinally grooved, general colour 

 dirty ivory-white mottled with pale brown, polished surface, 

 girdle banded. 



Anterior valve. — The apex and nearly half the valve 

 smooth, the rest radially ribbed, which ribs are broken with 

 concentric grooving. I counted eighteen ribs. 



