240 NATURAL SCIENCE. April, 



[ = Cypnna] islandica would separate it from the Veneracea ? When, 

 however, one of the foremost of living conchologists, and a careful 

 naturalist of world-wide reputation like Dr. Dall, comes forward with 

 a scheme founded primarily on the hinge-characters, it is natural to 

 turn with expectancy to his paper in anticipation that some clue to 

 the problem, and one satisfactory to the palaeontologist, has been 

 found. Dr. Dall, however, cannot, and does not, attempt to satisfy 

 the demand for an infallible scheme based on the hard parts ; all he 

 can do is to adopt " such an arrangement as shall," in his opinion, 

 " best express the relation of the groups, and at the same time take 

 into account those characters which are available for the palaeonto- 

 logist"; and of his three principal groups, he says, " they were based, 

 not on the forms of hinge-teeth as such, which would have brought 

 together many incongruous forms and separated near relatives, but 

 on the development of a general type in each case, to which, in spite 

 of present superficial incongruities, the pedigree of existing genera 

 could be referred." 



At the same time, there is no doubt but that a very great deal 

 more has yet to be made out concerning the morphology of the hinge 

 in the Pelecypoda. To begin with, the nomenclature requires over- 

 hauling ; there are instances in which teeth are set down as cardinal 

 that would appear to be lateral in origin although cardinal in 

 position, owing to the contraction of the hinge area, as in some of the 

 Veneracea, while secondary laterals have in some cases been developed 

 in order to prevent the valves from shifting when closed. This is partly 

 recognised by Dall, who calls these latter, if well developed — " teeth," 

 and, if less pronounced — "laminae." Of course, it is at times extremely 

 difficult to say where the line should be drawn between a slight 

 thickening or shelly prominence and a tooth, for these vary even in 

 the species of a genus, and hence the necessity for examining every 

 species of a genus, as Dr. Dall has evidently in many instances done, 

 and not the typical forms only. 



[Since the above paragraph was written, a most valuable paper 

 by M. Felix Bernard (15), of the Paris Museum, has come to hand, 

 showing that he has recognised the importance of these very points, 

 and is dealing with the hinge in its morphological aspect. See Nat. 

 So., viii., p. 153.] 



The necessity for a clear understanding on the terminology 

 becomes all the more important when use is made of formulae such as 

 those of Steinmann, for unless carefully and consistently drawn up, 

 they are apt to lead, when employed for purposes of comparison, to 

 erroneous results. A propos of these formulas, it is interesting to note 

 that the principle is much older than Steinmann's work (19), having 

 been put into practice by Professor H. G. Seeley in 1864 (16) as an 

 extension of the idea foreshadowed in Woodward's Manual (18). 



On the whole, Dr. Dall may be said, in his classification, to 

 approach the question rather from the standpoint of the systematist, 



