4 NATURAL SCIENCE [January 



received {Bull. Soc. Geol. France, ser. iii., torn, xxv., pp. 559-66, 

 figs.). In the third note (vide Nat. Sci., vol. x., p. 88), he dealt 

 with the Anisomyaria, in the present one he deals with certain of 

 the Heterodonta which had been passed by in his first note. The 

 Unionidae, however, still remain to be studied. The author finds 

 that the Heterodonta naturally fall into two groups which he pro- 

 visionally, and without at present attributing any taxonoraic value 

 to them, calls the ' Lucinoid ' and the ' Cyrenoid.' To the former he 

 now refers the Cardiidae (cockles), Donacidae, Corbulidae, the Tel- 

 linacea, the Pholadidae, Trigoniidae, and Dreyssensiidae. 



This decision as regards the last-named family is very important, 

 in that it confirms the conclusions of competent anatomists that it 

 was not, as always previously maintained, allied to the Mytilidae. 

 The Chamacea and Eudistes prove a highly interesting group with 

 respect to their development, for the hinge of the normal Cliama is 

 in its early stages Lucinoid ; in the ' reversed ' individuals, on the 

 other hand, and in the Diceratidae, it is Cyrenoid, whilst in the 

 Eudistes there is great diversity. 



We still await with interest the yet promised monograph on the 



whole subject. Meantime, those who care for the study will find 



^;(^ some very important theoretical suggestions in Mr Bernard's paper 



\ot^ on Conchylocardia (Journ. de Conchyl., July 1896 [1897], 1 pi., 



-^") figs.). 



These minute little bivalves, the largest of which only attains 

 in its maximum diameter 1.3 mm., constitute a new type of 

 pelecypod, and in their hinge present an early stage of the develop- 

 ment of that in the Carditidae, Astartidae and Crassatellidae, 

 especially the first-named. Not that they are to be regarded as an 

 ancestral form ; on the contrary, Mr Bernard considers the case to 

 be one of neoteny (or paedogenesis). The genus would be de- 

 rived from a normal type of Cardita, in which reproduction began 

 early and which would thus be arrested in its growth. A similar 

 condition of affairs is manifest in Philohrya, which genus forms the 

 subject of another paper {Journ. de Conchyl., Jan. 1897, 1 pi., 

 figs.). Hochstetteria, if not generically identical with this, is at 

 least very nearly allied indeed, and both present close affinities with 

 the Aviculidae. Dall has stated very positively (so much so that 

 we have quoted it as a fact — vol. xi., p. 341) that Philohrya 

 passes through a glochidial stage; but it appears that this was an 

 ingenious but unverified hypothesis based on an apparent similarity * 

 in shape between the young shells of this genus and of the Union- 

 idae. Yet another paper by Mr Bernard {Ann. Sci. Nat. Zool., 

 s6r. viii., tom. iv., pp. 221-52, 2 pis., figs.) describes the detailed 

 anatomy of Chlamydoconcha orcutti, Dall, which might be described 

 as a marine bivalve slug, for the two valves of the shell are reduced 



