joiV'nil ApmTmo.'] I^oyal MierosGopcal Society. 181 



About two years ago I received from Mr. Meek, of Washington, 

 U.S., through Mr. Davidson, some very well-preserved specimens of 

 FusuUna, from the Carboniferous Limestone of Iowa ; an examina- 

 tion of which has fully confirmed my previous belief as to the per- 

 forate structure of its shell, whilst it has also enabled me to make 

 such a precise measurement of the size of the pores, and of their 

 distance from one another, as will settle, in my opinion, its j)recise 

 place in the Vitreous series. 



The exceptional condition of these specimens arises from their 

 having been imbedded in a matrix — not of Limestone, but of a mix- 

 ture of Sand and Clay ; from which they can be detached without 

 difficulty, presenting, when thus freed, an aspect which seems to 

 differ very little from that by which they were characterized when 

 living. Those who are acquainted with the difference in condition 

 between the NummulUes of the Bracklesham Clay, and those whose 

 aggregation makes up the purely calcareous beds of the Nummulitic 

 Limestone of Southern Europe, will at once understand the import- 

 ance of the character of the matrix, when the question is one of minute 

 texture. My own early investigations into the structure of Nuimnu- 

 lites* were fortunately made upon Bracklesham specimens, kindly 

 placed in my hands by Dr. Bowerbank. Had I commenced with 

 studying sections of Nummulitic Limestone, I might have worked 

 long and toilsomely without discovering the fine tubulation, the 

 traces of which, in Nummulites imbedded in a calcareous matrix, 

 are usually almost extinguished by metamorphic action. 



The Iowa specimens of FusuUna came from two localities, about 

 forty miles apart, but on the same Geological horizon; and they 

 form two series very distinct from each other, alike in size and in 

 complexity of structure. That this difference (which is comparable 

 to that which I have pointed out between the Simple and the Com- 

 plex types of Orbitolite) is not one oi Age, seems very clear from the 

 fact that all the large and complex specimens come from one locahty, 

 and all the small and simijle forms from the other. And I cannot 

 help thinking that the results of the researches on which I have 

 lately been engaged, as to the diverse Temperatures met with on the 

 same sea-bottom at corresponding depths within a few miles, throw 

 considerable light upon cases of this kind, which, when the attention 

 of Palaeontologists is once directed to them, may prove by no means 

 unfrequent. 



The general structure of the small and simple type, of which the 

 largest specimens are about 0*18 inch in length and ■ 05 inch 

 in diameter, corresponds so closely with that of the simple type of 

 which internal casts were figured by Prof. Ehrenberg f under the 

 designation Borelis, that there is no occasion for me here to say 



* ' Quai'terly Journal of the Geological Society,' vol. vi. (1S4'J), p. 22. 

 + ' Mikiogeologie,' plate 37, fig. xi. See also ' Introduction to the Study of 

 the Foraminifera,' plate xii., fig. 24. 



