614 



SCIENCE. 



[N. S. Vol. XIX. No. 485. 



conclusion is not unexiDected by those who 

 have carefully examined the evidence, both 

 geological and faunal. The data of zoogeog- 

 •raphy are wholly at variance with Spencer's 

 hypotheses involving oscillations of gigantic 

 Vertical amplitude within late Neocene time. 



To the paleontology Dall has brought to 

 Ibear the experience of a life-long study of 

 recent mollusca, an advantage possessed by 

 few, if any other, writers upon American fos- 

 sils. This has led naturally to a juster ap- 

 preciation of the morphologic problems en- 

 countered than has been possible to most 

 paleontologic authors, whose acquaintance with 

 living mollusks is, as a rule, largely at second 

 hand — from the manuals rather than the 

 things themselves. With the gTeat collection 

 of recent American marine mollusks in the 

 National Museum, the material for exact com- 

 parison of the fossil and existing forms was 

 always at hand, and a vast number of correc- 

 tions and rectifications of all sorts, in the 

 nomenclature and classification of both recent 

 and Tertiary mollusks have been made. This 

 gives the work fully as much value to the 

 student of existing faunas as to the paleon- 

 tologist. 



During the progress of the work a new 

 classification of the bivalve mollusks (Pele- 

 cypoda) has been elaborated, a separate part 

 being devoted to an exposition of the general 

 system of pelecypods. Whether or not this 

 classification will eventually supersede that 

 of Pelseneer, which at present is generally 

 adopted abroad, it possesses certain manifest 

 advantages for the paleontologist over that of 

 the Belgian zoologist, in that the hard parts, 

 which alone are preserved as fossils, are taken 

 into account. The work of Newmayr, the 

 researches of Bernard and others upon the 

 ontogeny of the bivalve hinge, and the phylo- 

 genetic studies of Dall himself, all indicate 

 that the several elements of the hinge with its 

 interlocking processes or ' teeth ' are the bio- 

 logical expression of stresses to which they are 

 subjected in the individual. The evolution of 

 these wonderfully adapted structures has been 

 in part worked out, so that the great part 

 played by parallel or convergent evolution, 

 hitherto hardly taken into account by paleon- 



tological students of bivalves, is now exposed, 

 and sound phylogenies become possible. 



Those who oppose the major divisions of 

 Dall's classification will admit that the mar- 

 shalling of the families into superfamily 

 groups, and the internal analyses of these 

 groups, has been accomplished with the con- 

 summate skill of a master. 



In many groups of bivalves the classification 

 down to genera and subgenera is worked out 

 for all known forms, so that the work is a 

 general manual of the subject, often with an 

 entire recasting of the groups and their defini- 

 tions, as in the MaCtracea and Leptonacea 

 (Parts IV. and V.). The treatment of the' 

 Veneracea and allied groups in Part VI. is 

 equally elaborate, though less completely rev- 

 olutionizing prior conceptions. 



The matter of nomenclature has received 

 great attention, and as a general rule the nu- 

 merous changes of current usage have been 

 made with excellent judgment. In some cases, 

 such as that of Pisidium, it would seem that 

 Dall has gone more than half way to meet 

 trouble; while the emendation of some other 

 names for the sake of Latin form will not be 

 received with general enthusiasm. Thus if 

 Pitar Homer (1857) is barred from acceptance 

 because of its derivation from a West African 

 tongue, it can not be used as a generic name 

 in the form Pitaria (Romer) Dall (1902), be- 

 cause several other names were applied to 

 members of the genus between these two dates, 

 one of which would lead as a generic term. 

 Plere, as usual in such cases, it seems best to 

 accept a generic name as it was coined, even 

 if it is bad Latin. Little advantage or glory 

 comes from breaking lances against such wind- 

 mills. 



An interesting and valuable point to the 

 evolutionist is the persistence through long 

 periods of characters apparently trivial — now 

 a minute lamella or tubercle in the hinge, now 

 an external sculpture-pattern or an internal 

 sculpture, like the marginal grooving of 

 Transennella. What we have looked upon as 

 mere ' ornamentation ' has often suffered the 

 least change from age to age, and characterizes 

 the successive members of phyla which in 

 structures apparently far more important have 



