JUKES-BROWNE : SYNOPSIS OF THE VENERID^. 71 



from Ajitigona by the gradual elimination of the anterior laterals, 

 and I am quite disposed to think that such has been its oi'igin ; but 

 our genera are established for tlie sake of convenience in classification, 

 and not for the purpose of expressing a theory. There is no difficulty 

 in distinguishing the two groups and in recognizing them as genera, 

 and they have certainly had a separate existence ever since the 

 Miocene period. In the recent forms tlie anterior lateral is persistent 

 from youth to full age, and if tliere are fossil forms in which it 

 disappears with growth, they must be allocated on the sum of their 

 other characters, but I do not know of any. 



Here I must correct an error into which I fell in 1908 when 

 describing tlie Veneridae of the Eocene and Oligocene deposits. An 

 Oligocene shell described by M. iSt. Meunier under the name of Venus 

 loewiji ' was then ascribed to the genus Chione, because M. Cossmann 

 had referred it to that genus, and because reference to the published 

 figures seemed to show that such reference was correct. Recently, 

 however, by the publication of MM. Cossmann & Peyrot's Conchjlio- 

 logie Neogeniqtie de V Aquitaine, I became aware that their genus 

 Chione was the antiquated conception of Homer, and that it included 

 the groups of Claimna, Ot/qyhaloclai/mim, etc. In reply to inquiry 

 M. Cossmann informs me that his valves of Venus loewyi show 

 a distinct anterior lateral tooth in the left valve and a pit for its 

 reception in the right. It is clear, therefore, that the shell is a species 

 of Antigona, and does not belong to Chione ; it follows, moreover, 

 that Aniigona dates from the Oligocene period, and that Chione does 

 not, so far as we yet know. 



It may also be stated that tlie Ventricoloidea of Sacco (1900)* 

 appears to be a synonym of Artena, Conrad (1870).^ The type of the 

 former is Cytherea multilamella, Lam., and having compared specimens 

 of this shell, which I owe to the kindness of Professor Peyrot, with 

 the descriptions and figures of Artena given by Dr. Dall, I have no 

 hesitation in saying that it accords with Artena in all essential 

 particulars. As Dr. Dall remarks, Artena bears the same relation to 

 the typical Antigona {A. lamellaris) as Ventricola does to the group 

 which he calls Cytherea (i.e. A. piierpera), and this I understand to 

 be exactly the idea which Professor 8acco wished to express. 



It is unfortunate that the genotype of Antigona ( V. lamellaris, 

 Schum.) is so different from all the other recent members of tlie 

 genus that it stands by itself. It is one of the absurd results created 

 by the plan of fixing genera by 'types', and by the rigid rule of 

 priority that the so-called typical section of a large genus may 

 include only one species! Thi.s, however, makes no difference to the 

 definition of the genus as a whole, and I therefore give such 

 a description before indicating the various divisions of it. 



^ Nouv. Arch. Mas. cl'Hist. Nat. Paris, ser. II, torn, iii, p. 235, pi. xiii, 



figs. 11, 12. 

 2 I Moll. Terz. Piem., pt. xxviii, p. SO, 1900. 

 ^ Amer. Journ. Conch., vol. vi, p. 76. 



