April 20, 1900.] 



SCIENCE. 



623 



The Skulls of Syndyoceras and Protoceras: 



Erwin H. Barbour. 



The skull of the Oligocene Protoceras 

 with its many horns or protuberances was 

 compared with that of the four-horned 

 Miocene artiodactyl Syndyoceras. Though 

 representing widely divergent types, Syn- 

 dyoceras seems to be more closely related 

 to Protoceras than to any known form. 

 The main horn-cores or protuberances in 

 Protoceras seem to become true horn-cores 

 in Syndyoceras. The more prominent dis- 

 tinguishing characteristics of Syndyoceras 

 are the four grooved horn-cores ; the 'mid- 

 nares' or 'blow-hole' (of doubtful func- 

 tion) ; the tube eyes ; the incisiform canines 

 and the caniniform premolars of the man- 

 dible. 



Additional Notes on the Cladocera of Ne- 

 braska: Charles Fordtce. 

 Since the appearance of the two former 

 papers on the Cladocera of Nebraska (Por- 

 dyce, 1901 and 1904), the author has found 

 five additional species, which, added to the 

 forty-five previously reported makes a total 

 of fifty species thus far reported from Ne- 

 braska. The species described in this paper 

 are embraced in the following three fam- 

 ilies: DaphnidiE one, Bosminidse one, Lyn- 

 ceidffi two. The additional species are as 

 follows : Simocephalus serrulatus n. var., 

 Bosnima n. sp., Alona quadrangularis 0. F. 

 Miiller, Pleuroxus hamatus Birge, Pleu- 

 roxus trigonellus 0. F. Miiller. These 

 forms are all new to Nebraska ; the first two 

 are new to science, and the last three are 

 rare in this country. 



The Accuracy of Acquired Habitual Move- 

 ments: H. L. HOLLINGSWORTH. 

 Contemporary psychology is paying in- 

 creased attention to the general subject of 

 movement. While the psychophysics of 

 inactive perception has become fairly well 

 organized, the more active modes have dis- 

 closed less regularity and the need is felt 



for a more careful study in this field. The 

 comparison of series of naive and practise 

 tests of the accuracy of the standing, walk- 

 ing and sitting refiexes aifords the follow- 

 ing suggestions : 



(1) The lack of uniformity displayed by 

 modes of perception in which movement is 

 involved is due to the complex conditions 

 under which the movements are made, the 

 general activity of the refiex, its functional 

 correlation with static and orientation 

 sense, etc. (2) The extremely delicate dis- 

 crimination possible to even the most mas- 

 sive reflex is worthy of remark. (3) There 

 is a practical minimum below which the 

 threshold can not be reduced, and this 

 threshold is about the same for all indi- 

 viduals. (4) Practise results may be mani- 

 fested either in the reduction of the thresh- 

 old, or, if the threshold remain constant, in 

 the gradual definition and increased cer- 

 tainty of the criteria of judgment. (5) 

 The more activity involved in a movement, 

 and the more closely connected it is with 

 static perception, the more susceptible is 

 the movement to the reduction of the ob- 

 servable difference threshold by practise. 

 The less activity involved the more likely 

 is practise to result in the definition of the 

 criteria. (6) The correlation of sensory 

 and motor factors in the process of learn- 

 ing is seen to be advantageous. The more 

 activity involved in an act of learning, the 

 more quickly will the process be mastered. 

 Since motor correlations are in general 

 more persistent than sensory, it is also prob- 

 able that the acquirement will be longer re- 

 tained. 



The Composition of Some Unique Feeding 

 Stuffs Used in Nebraska: S. Avert. 

 The following unique feeding stuffs were 

 analyzed: burned alfalfa, the soapweed of 

 the sand-hills, a water plant known as horn- 

 wort, and the much-abused Russian thistle. 

 Bifrned alfalfa loses about 700 pounds, 



