210 G. M. Dawson— Foraminifera, etc. 



20 fathoms, and continues from that point increasing in num- 

 ber and size to the depth of 50 fathoms, which is the greatest 

 1 ., • ^ , ^ . , . . , 'ad. 



Id tend, with 



other facts, to show that these organisms, together with most 

 other marine animals of low organization, do not depend, to any 

 great extent, on the depth or intensity of daylight, but almost 

 entirely on the temperature of the water, as Dr. Carpenter main- 

 tains in his account of his recent deep-sea dredging, so that thev 

 would not giye very satisfactory evidence of the conditions ot 

 deposits of Post-pliocene or other beds, unless other facts were 

 at disposal to show the depth, when the Foraminifera woulJ 

 give valuable assistance with regard to the climatic conditions 

 at that depth. The quality of bottom has, however, much to do 

 with the general fades of the Foraminifera, as with other ani- 

 mals. For, as shown above, calm water, with a bottom com- 

 posed of fine sand and sediment, is particularly favorable to the 

 arenaceous forms, though, even under these conditions, they do 

 not thrive in the very cold, deep water (such as tliat below 100 

 fathoms) in the open Grulf A stronL^ current at once causes all 

 sandy forms to disappear, mostly, no doubt, from want of the 



necessary 1 



ine materials : 

 preponderance of Trw^a.., 



The arenaceous forms, with t'lic (■xcc],tii)ii of those which are 

 tubular, constitute a series i)ar;illcl to tlic cnlcai-eoits forms, and 

 the members of which graduate into one another. It seems not 

 improbable that the individuals of the same species may assume 

 either appearance. It does not appear, however, that the same 

 individual can present both forms at successive periods. Un 

 the other hand, the sandy forms may really constitute a distinct 

 group parallel to the others. Sketches of some interesting 

 iorrns are given which do not appear to be precisely similar to 

 described species. These have been kindly examined \>J ^'■ 

 -Parker, of London, who regards the Lituola? represented in ngs. 

 1 and 3 as new species, to which he assigns the names Z. /««^"^ 

 and L cassis. The form represented in fig. 2 he regards as tiie 

 type of a new genus, to which, from the horseshoe-shaped tonn 

 of the aperture, he gives the name Rippocrepina, naming tpe 

 species K indivisa. 



