78 PROCEEDINGS OF THE MALACOLOGICAL SOCIETY. 



with it by some fossil species, both in Europe and America. It may 

 therefore be regarded as a section of Clausinella, wliich will thus 

 become a sub-genus of as mucii importance as Chione. In this apprecia- 

 tion of Clausinella I tind myself in accord with Messrs. Cossmann and 

 Peyrot, but they have made the mistake of including V. plicata in 

 the group and several fossil species which do not belong to it. 



My reasons for the elevation of the group named Protothaca by 

 Dr. Dall to the rank of a genus will be given in the sequel, but, 

 briefly stated, they are that when one species included in the group 

 by that author has been restored to Chione, and another one to Tapes, 

 the remainder form a small genus which can be satisfactorily defined, 

 and which seems to be intermediate between Chione and Tapes. 



Under the head of dementia it will be found that I have separated 

 certain recent species as a new section with the name of Terentia, and 

 I desire to thank Mr. MacAndrew for giving me the opportunity of 

 examining his specimens of these rare species. The Cretaceous 

 fossils, for whicli I created the sub-genus Flanentia in 1908, have 

 again occupied my attention, and the examination of the interior of 

 a left valve of Fl. ovalis, preserved in the Royal Albert ^[useum at 

 Exeter, has confirmed my opinion of the relationsliip between 

 Flaventia and dementia. 



I have included Clemefitiaand Ci/clina in this sub-family because of 

 their conchological characters, which, in the Lamellibranchs and for 

 the purposes of classification, I consider to be of more importance 

 than the small differences \vliich are observable in the animals within 

 the limits of a family. I am aware that Deshayes described the 

 animal of Clementia papi/racea as resembling that of Bosinia, and as 

 liaving completely united siplions and a compressed hatchet-shaped 

 foot ; so that if we trusted to the characters presented by the 

 animal of this species we might place dementia in the Meretricinae 

 near Bosinia or Pitaria, which latter, according to Adanson, has an 

 animal of similar structure. 



But we have no detailed information about other species of 

 Clementia. except that Dr. Dall has recently stated' that the animal 

 of CI. suhdiapliana (an American species) is 'veneroid'. He does 

 not explain what he means by this term, but it can only mean that 

 the siphons are wholly or partially free and that its foot is tongue- 

 sliaped, and he has consequentlv referred this species to his genus 

 Marcia (i.e. Samarant/ia). There can be no doubt, however, that the 

 shell and dentition of C. subdiaphana is more like that of Clementia 

 than that of Samarangia, and that it is still more different from the 

 fossils called Vetterella by Cossmann. Hence I agree with Carpenter 

 in regarding subdiaphana as a species of dementia, akin to C. vatheleti 

 and C. cumingi, and, if their animals differ from that of C. papyracea, 

 it may be convenient to establish them as a section or sub-genus. 

 Probably, however, the differences are no greater than those which 

 exist between different species of Tapes, as will be made manifest in 

 the sequel. 



' Nautilus for January, 1914, p. 103. 



