April It 1902. J 



SCIENCE. 



581 



the recognized rules of priority. When 

 for any group such diagnoses of the dif- 

 ferent subdivisions shall have been pub- 

 lished, and, after discussion, so modified 

 as to be acceptable to the majority of stu- 

 dents of the group, forms subsequently 

 described should be accompanied by sim- 

 ilar diagnoses and similar designations of 

 a type which will render them strictly 

 comparable to forms already known. 



The Hydracarini form a sharply limited 

 and very homogeneous group in which the 

 application of such a scheme as proposed 

 above seems practicable. Accordingly, it 

 is suggested here, and in the complete 

 paper it is expected that there will be 

 given for each family and genus : first, the 

 name having priority ; second the author of 

 the same, together with the date and exact 

 reference; third, a diagnosis in Latin and 

 English; fourth, the type, with reference 

 to the author and exact date, together 

 with the reasons for selection of the same. 



Southeastern United States as a Center of 

 Geographical Distribution of Fauna and 

 Flora: Chaeles C. Adams. (Read by 

 title only.) 



In general the geographical relationship 

 of the fauna and flora of the northern 

 United States, east of the Great Plains, 

 is with that of the Southeast, and points 

 to an origin in that direction, except in the 

 case of the distinctly boreal forms. The 

 abundance and diversity of life in the 

 Southeast indicate that it has been, and 

 now is, a center of dispersal. The relicts 

 indicate that it has been a center of pres- 

 ervation of ancient types, and the endem- 

 ism shows that it has been a center 

 of origin of types. There are two 

 distinct southern centers of dispersal in 

 temperate United States, one in the moist 

 Southeast and the other in the arid South- 

 west. Nine criteria, aside from fossil evi- 

 dence, are recognized for determining the 



center of origin or the locality of dis- 

 persal: (1) Location of the greatest dif- 

 ferentiation of a type; (2) location of 

 dominance or great abundance of individ- 

 uals; (3) location of synthetic or closely 

 related forms; (4) location of maximum 

 size of individuals ; ( 5 ) location of greatest 

 productiveness and its stability, in crops; 

 (6) continuity and convergence of lines of 

 dispersal; (7) location of least dependence 

 upon a restricted habitat; (8) continuity 

 and directness of individual variations or 

 modifications radiating from the center of 

 origin along the highways of dispersal ; 

 (9) direction indicated by biogeographical 

 affinities and (10) annual migration routes 

 in birds. There are three primary out- 

 lets of dispersal from the Southeast: (1) 

 The Mississippi Valley and its tributaries; 

 (2) the Coastal Plain, and (3) the Ap- 

 palachian Mountains and adjacent pla- 

 teaus. The first two have also functioned 

 for tropical types and the third for boreal 

 forms. Dispersal is both forward and 

 backward along these highways. It is 

 desirable to study individual variation of 

 animals and plants along their lines of 

 dispersal and divergence from the center 

 of origin, in such characters as size, pro- 

 ductiveness, continuity of variation, color 

 variation, and changes of habit and habit- 

 ats. Life areas should be studied as cen- 

 ters of dispersal and origin and hence 

 dynamically and genetically. 



Description of Cephalog animus vesicaudus, 

 sp. nov.: W. S. Nickeeson. (Read by 

 title only.) 



Fresh Water Polychwta: H. P. John- 

 son. 



The Lateral Line System of Polyodon 



spathida: Henry F. Nachtrieb. 



The paper considered only the general 



anatomical features of the lateral line of 



Polyodon. In general the systems of the 



