274 NATURAL SCIENCE. Oct., 



arenaceous species ; while still higher in the scale, and running 

 throughout the Turonian and Senonian zones (with but one exception), 

 Ammodiscus incertus remains apparently the sole representative. 



Turning now to the modern distribution — what is its nature and 

 special character ? The Textularian fauna is well marked up to a 

 depth of 400 fathoms, but beyond that depth the number of species 

 diminishes with remarkable suddenness, few being found at greater 

 depths, though those that occur have a very wide distribution. What 

 are the principal species which thus continue ? They are Textularia 

 agglutinans and T. giiadrilatera ; the former, as we have seen, a form 

 which passes into the Grey Chalk, whereas the species, now 



restricted to a depth of less than 400 fathoms, are mainly found in the 

 Chalk Marl or lower part of the Lower Chalk. ^ 



The species, however, which are associated with the above 

 Textularia give evidence of equal significance. - Certain forms of 

 arenaceous Foraminifera continue beyond the 500 fathoms. For 

 example, of those obtained by me, Haplophragmium agglutinans, 

 which ranged from the Cenomanian (Lower Chalk) into the Turonian 

 (Middle Chalk), has been obtained eight times beyond that depth. On 

 the other hand, it must be admitted that Haplophyagmiiim latidorsatum, 

 which has an equal distribution to-day, was only found by me in the 

 lowest zone of the Lower Chalk. According to my own investi- 

 gations, Gaudryina pupoides was similarly restricted, but from the 

 Richmond boring Professor Judd obtained this species associated 

 with Textularia agglutinans, in far higher beds of the Lower Chalk. 

 This species has been met with at the present day eleven times at 

 depths exceeding 500 fathoms, while Ammodiscus incertus, which I 

 have found in almost every Chalk zone examined (it being absent 

 only in the lowest zones of the Lower and Upper Chalk), occurs 

 five times at similar depths. 



The occurrence of the genus Ammodiscus is, in fact, a marked 

 feature in all modern deep-sea soundings, it having been reported no 

 less than twenty-two times from these greater depths, represented 

 mainly by three species, A . incertus, A . charoides, and A . gordialis, all 

 of which are constituents of the two upper divisions of the Chalk 

 series, though the first at present remains the sole representative of 

 its kind in the lower. 



What, then, are the broad results to be adduced from these 

 somewhat detailed considerations ? 



1. Many of the Cretaceous species of arenaceous Foraminifera 

 are specifically identical with those of the present day. 



2. Those species which are restricted to the Chalk Marl and 

 Lower Grey Chalk are those which occur to-day at depths of less 

 than 400 fathoms. 



1 At a depth beyond 500 fathoms one or both of these forms were obtained in 

 " Challenger " soundings eight times, other species only three times, and these were 

 of types unknown or exceedingly rare in the Upper Cretaceous. 



