22 NILS HJ. ODHNEK, STUDIES ON RECENT CHAMIDAE. 



department of the British Museum, I got an opportunity of procuring photographs 

 of the two specimens in question, showing their interiör with the dentition. An 

 examination of the photographs gave the following results: the »normal» form (fig. 

 10 a of Reeve, fig. 18 in the present work) has a hinge construction quite typical 

 for other »normal» Chamas, and the »inverse» shell (fig. 10 b of Reeve, fig. 19 here) 

 agrees in all details with other »inverse» forms. 1 As a consequence of the above 

 argument, the specimens, in spite of their similar exteriör sculpture and colouration, 

 belong to considerably different genera, and their referring to the same species is not 

 at all maintainable. 



This example clearly shows the risk and insufficiency of dealing only with 

 external characters when describing forms of Chamidae. From the striking resem- 

 blance of their rather peculiar sculpture and colouration Reeve was misled into 

 assuming their identity. And this is, indeed, not the only case of exteriör conver- 

 gence between the essentially divergent groups of Chamidae. Previously, Broderip 

 (1835) when constituting his Ch. imbricata referred to this species both dextral 

 and sinistral shells, but Reeve found them worthy of being kept apart specifi- 

 cally, and so he established for the dextral form the new species Ch. janus. From 

 Reeve's monograph may be obtained further examples to illustrate the confusing 

 parallelism in general shape, sculpture and colours between the two series of Chamas 

 (Chama s. str. and Pseudochama) perhaps above all Ch. venosa and P. janus. This 

 external similarit}^ caused Cooke (1886) to unite some »normal» Chamas, namely 

 M'Andrew's Ch. ruppelli (together with Ch. rejlexa and, possibly, Ch. foliacea) with 

 the »inverse» Pseudochama cornucopia. The named author says (p. 96): »However 

 much these four so-called 'species' may differ at first sight, yet careful examination 

 convinces me that the specimens (and they are many) all belong to one species and 

 to one only . . . Whether even the four species here supposed to be represented are 

 ultimately synonymous I do not discuss, being merely occupied with the species be- 

 fore me. 2 But any one who cares to examine the types in the British Museum may 

 note the exceeding similarity not only of these, but also of nivalis Reeve, brassica 

 Reeve and rubea Reeve. » 



A keeping together of the above-mentioned »normal» Chamas with the »in- 

 versed» PseudocJiama cormicopia is, however, as based only on the exteriör appearance, 

 inconsistent with the facts of the matter as shovvn here. Though bewilderingly alike, 

 the two groups must be kept apart, as they represent different types of hinge- 

 construction. No transitions between them can be established, nor have any species 

 been found in which the different hinge types are a mere individual characteristic. 

 All accounts of such occurrences are due to insufficient investigation. All exteriör 

 similarity between forms of either type is due to convergence. 



1 For this species 1 liave proposed (ef. Odhner 1917) the nainc Pseudochama similis, reserving Reeve's 

 naine fur the true Chama specimen, wliicli may be, otherwise, a variely of Ch. lärarn* Linné. 



2 Cooke was engaged in a ( ritical revision of M'Andrew's Mollusca from the Gulf of Suez. Having at 

 1 1 1 \ disposal some of the original specimens of Ch. re/lc.m and ruppelli as well as of P. cornucopia, all acquired 

 by Riksmuseum, I am able to settle, in coutrary to Oooke's statement of t lic identity of the two tirst-named forms, 

 the identity of Ch. ruppelli (as comprehended by M*Andrew) with Ch. iostoma Conrad; to the synonymy of Ch. 

 rcflexa is to be added Ch. porösa Clessin. 



