I 1(1 PALMER : 



taneous origin, and of a common history as regards that redu- 

 plication to which the progressive decrease in size is due. 

 This will then mean, that whatever the origin of the group 

 may be, reduplication within the group is simidiancous. 



This deduction is now confirmed by observation. Mr. F. 

 J. Keeley on May 2Sth, 191 1, collected A'^. socialis at Elam, 

 Delaware County. Pa., and found numbers of groups in pro- 

 cess of reduplication. The groups, being mounted in balsam 

 after burning on the cover glass, inevitably lay flat to the 

 view, so that the doubling of the frustules was not at once 

 evident : but by careful focussing it was possible to bring 

 into view the two old valves at top and bottom, and the two 

 new valves in the body of each of the four frustules. More- 

 over, an anomalous or unusual group of eight, in one of Mr. 

 Keeley's mounts, shows all of the eight in simultaneous divi- 

 sion. Following this observation, I have made new examin- 

 ation of my own mounts of the species, and have found sev- 

 eral instances of the same condition. I have yet to find a 

 case where only one or two or three of the individuals of a 

 group are in this state. Dislocated frustules (in material 

 that has been strongly boiled J freciuently exhibit, in girdle- 

 view, the aspect of reduplication familiar in other species, so 

 that we may safely say that the main facts of reduplication 

 of valves in this species are now clear. Subdivision is as 

 usual so far as concerns the individual frustule, and simulta- 

 neous in the members of a given group. The intimate nature 

 of the union is thus made evident, and brings to mind the 

 "group consciousness" of the psychologists. Mr. Keeley 

 further refers, in an informal communication, to the curious 

 alternation of the bending of the raphe terminations in the 

 neighboring valves of a given group, as is shown in the ori- 

 ginal figure.'*' This was carefully indicated by Miss Win- 

 chester, the artist, as a noticeable characteristic, general if 

 not uniform. Mr. Keeley has made countings, estimates 



*Proc. Acad. Nat. Sci.. IMiila., 1900. PI. XXXV, Fi^. i. 



