114 proceedings of the malacological society. 



Classification employed. 

 Since Evolution came to be accepted as a doctiiue It has been 

 a general policy to regard mere systematic work as a thing entirely 

 apart from the theoretical considerations of species formation. Hence, 

 in the bulk of zoological writings to-day a treatment of one involves 

 no co-ordination with the other, to the mutual handicap of each. The 

 first writer to break through these trammels of convention was 

 Alpheus Hyatt, and to him the modern classification of the Mollusca 

 is due. In the attempts to place this Phylum npon a stable footing 

 an ever-increasing number of students have laboured, important among 

 whom stand Jackson, Smith, and Grabau. Diverse as were the views 

 on species-change which these several writers held at the onset, in 

 recording the evolutionary modifications as they exist and applying 

 them in their systematic studies, all have arrived at essentially 

 identical conclusions, and the genetic classification ' has ceased to be 

 the unsupported theories of a philosopher-scientist and become a fact. 

 To quote Hyatt's Laiv of Jlorphogcnesis : "A natural classification 

 may be made by means of a system of analysis, in which the 

 individual is the unit of comparison, because its life in all its phases, 

 morphological and physiological, healthy or pathological, embryo, 

 larva, adolescent, adult, and old (ontogeny) correlates with the 

 morphological and physiological history of the group to which it 

 belongs (phylogeny)." 



Syntonia. 



Various writers, including Cooke- and Dall,^ liave noted the 

 occurrence, in the shells of freshwater molluscs from brackish or 

 enclosed bodies of water subject to concentration, of malleations, 

 plications, or scalarity among the Gastropods, arcuity and roughening 

 among the Pelecypods, and other deviations from the types found 

 under normal circumstances. These examples have been invariably 

 extreme instances, however ; the less striking ones pass unnoticed, 

 since hardly a lake, pond, marsh, slough, stagnant stream, semi- 

 estuary, or enclosed or partially enclosed body of water, contains 

 molluscs which are not more or less subject to these aberrancies. 

 Frequently, particularly in the arid regions of Western North America, 

 these forms have been redescribed as separate species,* but in no 

 instance are the characters inherited, though the stock may have 

 passed through a long line of abnormal generations. The progeny 

 under such conditions appear to be unusually liable to become 

 abnormal likewise, but this may be explained on the basis of hereditary 



^ Kecent accounts of the genetic classification and its application to Mollusca 

 may be found in J. P. Smith, Journ. GeoL, v, pp. 509-24, 1897; viii, 

 pp. 413-25, 1900; A. Giabau, Am. Nat., xxxvi, pp. 917-45, 1902; xli, 

 pp. 610-46, 1907. 



2 Mollusca, Cambridge Nat. Hist., vol. iii, p. 85, figs. 33, 34, 1895. 



3 Science, i, p. 202, 1883; Proc. Acad. Nat. Sci. Philad., p. 408, 1896. 



* Within a year one writer, evidently of limited experience in the field, has 

 distinguished as a distinct genus an extreme distortion of the common 

 Lymnaa auricularia from this region. 



