558 CLARK : GEOGRAPHICAL RANGE IN RECENT CRINOIDES 



minerals are associated with it. The general relations appear 

 quite similar to those in New Jersey. 



It seems quite remarkable that in New Jersey it should have 

 been formed in such abundance and in crystals of such great 

 size, and that later it should have been almost totally removed. 

 Its disappearance cannot well be ascribed to weathering, for in 

 many instances the casts have been filled with minerals of an 

 early period of deposition. The formation and subsequent 

 removal of the mineral indicate that for it the conditions of 

 chemical stability were satisfied for a brief period only during 

 the processes of general mineral deposition. 



ZOOLOGY. — The correlation between the hathymetrical and the 

 geographical range in the recent crinoids. Austin H. Clark, 

 National Museum. 



In a paper published about a year ago^ I remarked that the 

 geographical range of a crinoid species, genus or higher group is 

 approximately proportionate to its bathymetric range, but at 

 that time I did not have the facts upon which I based the de- 

 duction in such form as to be able to present them in a convinc- 

 ing manner. 



While the bathymetric range of any type can mean but one 

 thing — the number of fathoms (or meters) between the highest 

 and the lowest limit of the zone in which it occurs — the geo- 

 graphical range may be interpreted in two different ways: (1) 

 as the actual area, calculated as the sum of the geographical 

 units within which the type is actually known to occur, or (2) 

 as the area in which the type potentially occurs, that is, the area 

 over which physical conditions are such as to suggest .that, if 

 not found at all points within it now, it has or may have, occurred 

 at all points within it at some time in the not remote past. 



According to the first method a count is made of the units of 

 area within which the type has actually been taken; the figures 

 are therefore of very varying value for different groups, for many 

 types, undoubtedly with an enormous geographical range, have 

 been taken at only a very few widely scattered localities, while 



^ Internationale Revue der gesamten Hydrobiologie und Hydrographie, Bd. 

 6, Heft 1, S. 29. 



