236 proceedings: biologicaIv society 



between a species and a subspecies, because even very closely allied 

 forms are species, if their characters are trenchant and the birds do 

 not freely interbreed; while, on the other hand, however great the 

 differences may be between two forms, they are to be regarded as 

 subspecies if intergradation exists. 



Dr. N. C. Kendall's remarks were published in a recent number 

 of this Journal (9: 187. 1919). 



Dr. P. Bartsch speaking on the question with respect to moUusks 

 said: There are no hard and fast lines that can be invariably em- 

 ployed in deciding to which nomenclatorial category a certain form 

 should be assigned. He thought that in the present imperfect state 

 of our knowledge, most designations were largely a matter of judgment 

 and expediency. Systematists at present unfortunately recognize 

 only two categories, species and subspecies, by means of which they 

 attempt to designate all the products of Nature's laboratories. This 

 makes all sorts of compromises necessary in order to squeeze a given 

 form into|the one or the other of the two. It is his firm belief that 

 when the work of experimental biologists and breeders, which is heaping 

 up a pile of data, will have advanced a little further, we shall be furnished 

 with a mass of information which will demand recognit on of a larger 

 series of categories designed to express the true inwardness of phy- 

 logenetic relationship a little more definitely than it is expressed by 

 our present system of nomenclature. 



In many instances it is not difficult to decide the status of a form. 

 The old definition that "A species embraces an aggregation of indi- 

 viduals which may differ in age, sexual, seasonal or individual char- 

 acteristics" is easily enough applied in many instances; likewise can 

 be applied the definition for the subspecies, which simply makes it 

 necessary to have connecting elements between two such groups, 

 but what shall be done with a case like the following.'' 



"In the Philippine Islands we have, as far as known, only a single 

 species of Vivipara in a given region. In Lake Lanao, on the other 

 hand, we have apparently about forty. At all events there seem to 

 be that many constant forms, for the young which I have extracted 

 from probably more than a thousand individuals have always agreed 

 with the parents in sculptural characters. The range of form modi- 

 fications in these Lake Lanao viviparas can best be seen by consulting 

 my papers on the group. ^ Another paper on this topic is almost 

 completed. This is based on an examination of about 3,000 specimens. 

 What designation shall be given to forms like these ? These are probably 

 the result of cross breeding between two distinctly related stalks of 

 the genus. At least my Cerion breeding experiments would indicate 

 this. 



' The Philippine pond snails of the genus Vivipara. Proc. U. S. Nat. Mus. 

 32: 135-150. pis. lo and 11. 1907; Notes on the Philippine pond snails of the genus 

 Vivipara, with descriptions of new species. Proc. U. S. Nat. Mus. 37: 365-367. 1909. 



