KUNGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 59. N:0 3- 19 



of Tadjourah off the Red Sea. Both valves have, before their affixation, cuticular 

 hairs. The dentition is more like that of Echinochama, because there exists in either 

 valve a long lateral lamina, and in the dextral valve tvvo distinctly separated car- 

 dinal teeth. A single difference is offered by the absence of an anterior cardinal 

 tooth in the left valve (ef. Anthony, p. 316, fig. 41). 



After many futile researches with a view to getting small early stages of Chama 

 I found, among material collected on the north western coast of Australia by Dr. 

 E. Mj Öberg, a great many shells, together with specimens still preserving the soft 

 parts of the animal. The most abundant species of Chama in these collections was 

 Ch. jukesi (apparently a growth stage of Ch. rejletxa), and to this species the small 

 specimens turned out to belong, their identity being possible to establish by means 

 of a complete series of transitory stages. Those equal in size to the young ones of 

 Ch. reflexa described above (ef. tigs. 16, 17) exhibited the same characteristics in an 

 equal state of development. In still smaller shells (fig. 15) there were slight diffe- 

 rences. Especially, the crest representing tooth 1 was more obvious than in older 

 shells (ef. figs. 15 and 17). 



By observing a minute right valve of about 1 mm length I found this tooth 

 to be rather distinct as a comparatively short ridge of the same thickness as the 

 crest curving beyond it, representing the undifferentiated primary lamella III, the 

 origin of both 3 a and 3 b. This shell apparently represented the same stage as that 

 figured by Anthony (1905, fig. 41). This author, as is obvious from his designation 

 of the teeth, has overlooked tooth 1 inside the primary lamella III, and interpreted 

 the latter incorrectly, giving its foremost part the number 1 instead of 3 a, and the 

 back part of it the number 3 instead of 3 b. Even the manner in which Anthony 

 gives the formula of the hinge shows that he has incorrectly identified its elements; 

 the correct formula must be expressed in quite the same manner as for the adult 

 stage shown above. 



No anterior lateral tooth is found in the adult, nor does it appear during the 

 development, contrary to Bernard's statement (1895) that it may occur in certain 

 species of Chama. 



As to the exteriör characteristics of the young Chama these correspond, as will 

 be found from the figure 17, to those described by Anthony; the dissoconch ex- 

 hibits a sculpture of fine radiating riblets crossed by distant concentric lamellae. 

 On a free dissoconch observed by me in the material at my disposal, these lamellae 

 appeared to be more elevated on the posterior part of the shell. The dissoconch 

 sculpture was, just as Anthony states, abruptly changed into that of the definite 

 shell, consisting of irregular concentric rugations and scattered squamulae on the 

 posterior half of the shell. 



