182 Transactions of the [IZ'.'Jil "v;,?,?rK™' 



more in regard to it, than tliat it may be likened to a Nummuline 

 or a symmetrical Kotaline, of which the "alar prolongations" 

 extend themselves on either side in lines parallel with each other 

 and with the axis of the spire, instead of folding in towards each 

 other, as they do in discoidal shells. And m regard to the general 

 structure of the large and cotnplex type, of which the largest 

 specimens are about 0-30 inch in length and O'lS inch in 

 diameter, I have nothing to add to the description elsewhere given 

 (op. cit.) ; except that the irregularities which are noticeable in 

 sections made either longitudinally or transversely through the ter- 

 minal portions of the shell, seem explained by the disposition of the 

 alar prolongations which is revealed by fracture ; for this shows 

 that the alar prolongations, as they pass to a distance from the 

 median plane, tend to interdigitate with each other, in such a manner 

 as to produce great apparent confusion when they are brought into 

 view by section. 



It is, however, of the minute texture of the shell, that I have 

 especially to speak. This is generally much better preserved in 

 the Iowa specimens, than in specimens imbedded in a Calcareous 

 matrix ; but it is still often obscured by metamorphic action, the 

 calcareous infiltration which has penetrated the cavities of these 

 shells throughout, having also filled up the tubuli of their walls, 

 and so blended with the parietes of these tubuh that the line of de- 

 marcation between them is by no means distinct. Specimens occur 

 here and there, however, in which the shell-structure has been so 

 little altered, that the diameter of the tubuh, as well as their distance 

 from each other, can be accurately measured (Plate XLV., Fig. 6) ; 

 and I find their average diameter to be about 1-2 5 00th of an inch, 

 and their distance from one another to be equal to their diameter. 

 Thus they are intermediate in both respects between the Botalines 

 and the Nummulines ; approaching much more nearly, however, to 

 the former, whose tubuli are commonly about 1-2 00 0th of an inch in 

 diameter, and somewhat more than that apart from each other, than 

 they do to the latter, in which the average diameter of the tubuli does 

 not exceed 1-1 0,0 00th of an inch, their distance from each other not 

 being much greater. Fusulina departs, however, from the typical 

 Botalines, while it corresponds with the typical Nummulines, in 

 the perfect bilateral symmetry of its form, and in the position of the 

 aperture on the median plane ; thus adding another to the cases 

 now accumulating in great numbers, in which an earlier type pre- 

 sents a combination of characters which in later periods are dis- 

 tributed among several.* This combination I have shown to be 

 especially characteristic of EoziJon ; the organic character of which 

 I have now the satisfaction of finding all but universally admitted. 



* See ' Principles of General and Comparative Physiology,' 4th ed. (1854), 

 §§ 84-87. 



