KUNGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 59. N:0 3. 23 



On accoimt of the great difference between both groups their allying into a 

 single genus Chama is untenable, and they must be allotted to separate genera. 



It was Lamarck who, in 1819, first distinguished between the two groups of 

 Chamas, the one being characterized by »crochets tournant de gauche å droite», and 

 the other by »crochets tournant de droite å gauche». Afterwards the conception 

 normal» and »inverse» Chamas was created by Munier-Chalmas (1882) for the 

 respective groups; the first-named was so called because these forms are the most 

 comraon. For this group we have to retain the generic name Chama, not because 

 of the frequency of the species, but because it was on some of them (Ch. lazarus 

 and Ch. gryphoides) that Linné constituted his genus Chama in 1758. In 1767 Linné 

 established the species Ch. arcinelkt, which is referable to the dextral group of 

 Chamidae. 



The Lamarckian distinction was abandoned låter on, when Broderip established 

 his Ch. imbricata in 1835, to which he also referred a dextral shell which he con- 

 sidered as a young specimen. This »species», however, was shown by Reeve in 

 1847 to comprise two distinct ones, Ch. janus in addition to Ch. imbricata, and 

 Reeve remarks that the direction of torsion is constant in every single species with 

 the exception of his Ch. pulchella which, however, as we found above, also hickades 

 two species. This misinterpretation of Reeve's has causecl his view of the Chamas 

 as a uniform genus to be retained, so that even the most modern authors repeat 

 the statement that it contains forms of different torsion. Thus Dall (1895, p. 542) 

 says: »Either of the valves of Chama may be the sessile one, but the teeth in the 

 fixed val ve, whether right or left, are always the same, and similarly with the free 

 valve.» Anthony (1905, p. 288) states that »chez les Chames, la fixation se fait 

 tantöt par une valve, tantot par 1'autre . . .», but he remarks in a note: »D'aprés 

 Woodward dans certaines espéces de Chames la valve fixée serait indifférement la 

 droite ou la gauche; je n'ai jamais rien constaté de semblable. » Pelseneer (1911, 

 p. 58) says: »Les espéces de ce genre ne sont pas toutes fixées sur le cöté gauche: 

 il existe des formes 'inverses', fixées par le coté droit . . . (dans Ch. pulchella Reeve 

 d'Australie, la fixation se ferait indifféremment sur l'un ou l'autre coté).» 



We have just stated that the »normal» Chamas have priority for bearing this 

 generic name. For the so-called »inverse» forms, which have been found to develop 

 from a separate type and thus are not at all »inverse», a nevv genus must be created 

 as a result of the above arguments. For the most symmetrically shaped of them a 

 separate genus, Echinochama, was established by Fischer in 1887 (= A rcinella Scnu- 

 macher 1818). As this genus was based on the characters peculiar to the single 

 species E. arcinella (to which Dall added a few new forms låter on), I find it most 

 convenient to keep it restricted as a sub-generic name for these rather character- 

 istic forms only, though in their essentials (hinge construction) they constitute typ- 

 ical members of the hitherto so-called »inverse» group. As a comprehensive name 

 for this whole group, which is, as it seems, a well defined genus, I have proposed 

 (in 1917) Pseudochama, a name which refers to the misleading phenomenon of con- 

 vergence to the genus Chama in its new, restricted, sense. 



