46 C. R. Eastman — Preliminary Note on the Relations 



water occurred simultaneously with them all, the main river 

 I would have to carry over three millions cubic feet of water per 



I second to the Grulf. As a matter of fact, it is an extremely 



rare coincidence for more than two of the large tributaries to 

 be at their highest yearly stages at the same time. The 

 greatest annual flood upon the Ohio, for example, has disap- 

 peared before that from the Missouri reaches the Mississippi. 

 I Thus the aggregate in the main river is kept down, so that 



1,800,000 cubic feet per second may be considered a large flood 

 discharge from the Mississippi. The combination of condi- 

 i tions is such that the lower river usually reaches its maximum 



volume for the year in April or May, and its lowest stage in 

 October or ]^ovember. The diagram shows, by a convenient 

 comparison of rates of flow per square mile per second, the 

 resultant effect of all the tributaries upon the main river. The 

 ; rate of low flow, 0"139 cubic feet per square mile per second, 



' is fairly well up, in spite of the downward pull given by 



the Missouri and Arkansas. The rate of high flow is kept 

 down to 1-4:3 cubic feet per square mile per second, — which is 

 only surpassed in smallness in the case of the Missouri, — by the 

 above mentioned lack of coincidence in the times of flood from 

 the various tributaries. 



Art. YL — Preliminary Note on the Relations of Certain 

 Body-plates in the Dinichthyids / by C. R. Eastman. 



Thanks to the energy and skill of the local Ohio collectors 

 in bringing together and developing fresh material, and to the 

 painstaking descriptions of Newberry, Claypole, Wright and 

 others, palaeontologists have gradually become familiar with 

 the principal features of Dinichthyid anatomy. Few chapters 

 in the history of American palaeontology are more interesting 

 or instructive than that relating to the discovery and syste- 

 matic fitting together of the detached parts, as rapidly as each 

 new piece was brought to light, until finally almost the entire 

 skeleton of these huge Arthrodira has been accurately recon- 

 structed. For skill in determining isolated fragments and 

 assigning them to their natural position, and for sagacity in 

 tracing out the homologies with European Coccosteans, the 

 work of these authors leaves nothing to be desired ; and so 

 thoroughly has every scrap of material been overhauled and 

 scrutinized in the search for new evidence, that the structural 

 details which still remain to be completed are relatively insig- 

 nificant. 



The object of the present paper is to communicate a slight 



