68 PROCEEDINGS OF THE MALACOLOGICAL SOCIETY. 



removal of some adherent sand in order to expose their pedal scars, 

 has induced me to change my opinion so far as the relationship to 

 Meretrix is concerned. 



I find that in both species tlie pedal scar is small and separate 

 from that of the adductor, a feature which is not found in any 

 Meretricine genus except Circe. The cardinal teeth, being straight, 

 separate, and nearly equally divergent, also resemble those of Circe 

 (especially of Gutddia) quite as much as they do those of Meretrix; 

 but Meretrism differs from both in exhibiting a small pallial sinus 

 which is more than a mei'e inflection of the pallial line, though it is 

 not deep. 



Further, since Circe, in the forms of Circenita and Gouldia^ co- 

 existed with Tivelma, while Meretrix has not been found in any of 

 the European Tertiaries, I now consider Meretrissa to be more closely 

 allied to Circe than to Meretrix. It may be regarded as a link 

 between Tivelina and Circenita, but, as the internal features resemble 

 the latter more than the former, I group it here as a sub-genus 

 of Circe. 



Shell small, sub-trigonal, nearly smooth, compressed. Hinge weak 

 with three divergent cardinals, the anterior of the right valve 

 pointing to the anterior lateral pit, the median grooved, and the 

 posterior entire. Pallial line with a short rounded sinus. Pedal scar 

 separate from adductor. 



Genus Meketrix, Lamarck, 1799. 



This genus is very distinct both in general form and in dentition 

 from all the preceding genera, and it is, therefore, far from being 

 a good type of the sub-family to which it gives its name. The species 

 of which it consists are few, and they are restricted to the Indian and 

 Chinese seas, extending from Aden and tlie Gulf of Oman to Timor 

 and the Philippines, and as far north as Japan ; but I have not been 

 able to find any record of its occurrence in Australian waters, nor in 

 the Pacific Ocean, nor have I been able to ascertain how far it reaches 

 southward along the east coast of Africa, but it does not exist in 

 Natal or Cape Colony.^ 



Moreover, it appears to be of comparatively recent origin, for it 

 does not occur in any of the Tertiary faunas of Europe, neither can 

 I find that any ancestral foi'm has been described from those of India 

 or Eurmah. At present, therefore, it seems impossible to say when 

 or where it originated, but its distribution suggests that its centre of 

 dispersal was either from Siam or the Malay Archipelago, for most 

 of the species are found in that region. 



^ Meretrix lusoria has been recorded from Natal by Mr. G. B. Sowerby (Journ. 

 Conch., 1894, p. 377), but he subsequently found that it was really 

 a species of Tivela, and in his Appendix to Marine Shells of South 

 Africa, published in 1897, he described the species under the name of 

 Tivela alucinans. In 1903 (Proc. Malac. Soc, vol. v) Mr. E. A. Smith 

 identified it with Tivela natalensis of Dunker, and he informs me that 

 •it was by mistake that the name of Meretrix zonaria was included in the 

 same list, the shell being really T. natalensis. 



