KUNGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 59. N:0 3. 17 



one tinverse» Chama species occurs, viz. gryphina, in the Mediterranean. By means 

 of the valves fourid, a continuous series of young stages could be established. 



With regard to the exteriör characteristics of the nepionic shell, both valves 

 (figs. 9—10) are of a similar shape and sculpture; they show a prominent papillary 

 umbo and distant coneentric laminae, which project on the posterior part as concave 

 squamiform spines. For the rest the shell exhibits an extremely minute punctate 

 texture. These exteriör characteristics alone remind one vividly of Echinochama, as 

 does the shape of the umbonal region of the adult shell. 



Even the construction of the hinge is strikingly similar in both species. In a 

 left valve of I.07 mm (fig. 10) there exists a median large cardinal of a trigonal 

 shape, descending inwardly, and before and behind it a short but distinct anterior 

 and posterior cardinal; a verv small posterior lateral tooth is also traceable. In the 

 right valve (fig. 9) two divergent cardinals of uniform size are situated in front of 

 the socket, and behind it a short and narrow posterior one. A very strong posterior 

 lateral tooth is to be observed behind the end of the ligament fitting inside the 

 left lateral. There are no anterior laterals in either valve. 



In a recently attached valve of 1.4 mm length (fig. 11) the hinge construction of 

 the nepionic stage still prevails in its essentials as shovvn by the occurrence of two 

 separate cardinals. These now arise from a common callosity projecting from the 

 dental margin. Behind them one perceives the socket and the third cardinal, and 

 lastly the lateral tooth, which is considerably smaller in comparison with the other 

 teeth than it is in the nepionic stage. 



A specimen about three times larger (fig. 12) shows the callosity bearing the 

 two anterior cardinals considerably increased, so that the primary tooth appears 

 merely as a pair of swellings separated by a shallow and narrow furrow on the 

 upper and inner side of the callosity. The third (posterior) cardinal retains its indi- 

 viduality and has increased in length, but the lateral is relatively still more reduced. 



Lastly, in the full-grown shell, it may happen that the two right anterior 

 cardinals are still distinct, though small, and that the left cardinal tooth fitting 

 between them is still present. That is the case, for example, in one specimen, which 

 comes fronjy Zara in Dalmatia. Most frequently, however, the dental callosity of 

 the right valve attains the shape of an entire dental formation, because the teeth 

 finally obliterate by the deposition of lime substance. This circumstance has caused 

 the misinterpretation of the callosity as a^real tooth ; its origin, however, which is 

 shown here, clearly proves that its nature is due to a composition of two primary 

 teeth. 



As to the laterals, we find in the adult shell the right one persistent though 

 very small. The left lateral, which in the young shell is fitting outside the right 

 one, is entirely reduced and is replaced by a small marginal tooth, received inside 

 the right lateral, quite as in Echinochama. 



The facts now described, as well as the morphology of the new form Pseudo- 

 chama pusilla described further on, allow us to identify the elements of the hinge 

 in the »inverse» forms of Chamidae. We must understand that the anterior »tooth» 



K. Sv. Vet. Akad. Handl. Band 59. N:o 3. 3 



