May 5, 1899.] 



SCIENCE. 



64B 



especially deepened. This places them 

 among the more primitive members of the 

 genus, and hence would seem to indicate a 

 Lower Jurassic horizon. 



The distribution of American Devonian 

 fishes was discussed with reference to those 

 of other countries. During the Lower De- 

 vonian there was none, and in the Upper 

 scarcely any intermingling of United States 

 and Canadian vertebrate faunas, but those 

 of Canada and Great Britain belonged to a 

 distinct province. Corniferous fishes of 

 Ohio and New York are most nearly related 

 to those of the Middle Devonian of con- 

 tinental Europe, especially the Eifel, Bo- 

 hemia, etc. The Hamilton faunas of New 

 York and the Mississippian region, includ- 

 ing Manitoba, are the direct successors of 

 the Corniferous, but the Chemung of both 

 eastern and western regions (or its equiva- 

 lent) contains a remarkable mixture of in- 

 digenous types and intruders from all direc- 

 tions. Intercommunication between eastern 

 Canada and Great Britain, Spitzbergen, 

 etc., became general for the first time dur- 

 ing this period. The transition between 

 Devonian and Carboniferous faunae is now 

 known to be more gradual than was for- 

 merly supposed. 



The only natural basis of family classifi- 

 cation among Arthrodires was held to be 

 through comparison of the sutures of cranial 

 and dorsal shields, the differences in denti- 

 tion being of only secondary importance. 

 Degeneracy of the latter in Titanichthys, etc., 

 is paralleled by that in certain toothless 

 whales (^ilesoplodon, etc.) . Cranial osteology 

 of Homosteus and Heterosteus compel their 

 removal from Coccosteidm to form a separate 

 family called Homoateidce. In this family 

 the so-called antero-dorso-lateral corre- 

 sponds to the like-named element in Di- 

 nichthys and Titanichthys plus the clavicular. 

 The latter plate functioned as a support for 

 the gills, and hence may be interpreted as a 

 modified branchiostegal apparatus, but in 



no sense as a part of the shoulder-girdle. 

 There is no evidence that any of the Ar- 

 throdires possessed pectoral fins. The ob- 

 vious resemblance of this group to Ostraco- 

 derms, with implied relationship, is lost 

 sight of through its removal by Woodward 

 to the Dipnoi, and there seems to be suf- 

 ficient evidence for regarding the Arthrodira 

 as a distinct sub-class, of equal rank with 

 Lung-fishes, Teleostomi, etc., as already 

 suggested by Dean. 



Charles R. Eastman. 



RAPIDITY OF SAND-PLAIN GROWTH* 

 The undisturbed character of the strati- 

 fied deposits making up the sand-plains, 

 taken in connection with the absence, or at 

 most, the very slight development of con- 

 structional back-sets, indicates, as was early 

 pointed out by Davis, a stationary ice 

 margin during the period of deposition. It 

 follows, therefore, that their formation must 

 have been extremely rapid, and the natural 

 conclusion is that they represent the de- 

 posits of a single summer's period of melt- 

 ing, an interval not over eight months in 

 length. 



It occurred to me that a calculation based 

 upon the conditions now existing in the 

 large glaciers of Alaska might give some 

 indication as to the probability of such 

 estimates, or at least would be of interest in 

 this connection. 



To make this calculation it is simply 

 necessary to divide the bulk of the sedi- 

 ments by the daily discharge of detritus by 

 the glacial stream which deposited them. 

 This involves factors which are usually very 

 diflBcult to determine, but at the sand-plain 

 near the railroad station at Barrington, 

 R. I., the conditions are almost ideally per- 

 fect, and admit of the determination with 

 considerable accuracy of both the bulk of 



* Abstract of paper read before Boston Society of 

 Natural History, February 15, 1899. 



