GENUS CYCLOCLYPEUS. 297 



This independence is strikingly manifested by the frequency with which incomplete annul i 

 are added to the previous margin of the disk, extending (it may be) along not more than a 

 third, a half, or two thirds, of the entire circumference. Thus the growth of Cjjclucli/peu.i is 

 in reality rather radial than cyclical ; the formation of concentric rings being simply due to 

 the fact that the sub-segments occupying the last-formed annulus of chamberlets are for the 

 most part ready to originate a new series of chamberlets at the same period. This restriction 

 of the communication between the different parts of the sarcode-body, which is in such 

 marked contrast with the extreme freedom that prevails throughout OrbifoUtes, is probably 

 related to the circumstance that whilst the aggregate animal of the latter is nourished by the 

 pseudopodia protruded through the marginal pores alone, each sub-segment of the former 

 may imbibe its nutriment by pseudopodia passing through the tubuli of the walls of its own 

 chamber (^ 59). Tiiat these tubuli, notwithstanding their minuteness, serve for the passage 

 of pseudopodia, and that these pseudopodia may coalesce on the exterior of the disk into a 

 layer of sarcode forming a continuous investment of its surface, appears from the fact that 

 successive laminre are added to the e.rfcrior of the shell, the tubuli of which are continuous 

 with those of the laminae to which they are applied, — a fact which can scarcely be explained 

 on any other supposition. 



500. Thus, then, whilst in the isolation and independence of the subdivisions of its 

 body, in the enclosure of each of them in its own proper wall, in the interposition of an 

 intermediate skeleton and of a canal-system between the contiguous walls of adjacent 

 chamberlets and annuli, and in the minutely-tubular structure of the shell, — all of them 

 points of high physiological importance, — Cycloclijpeus agrees with Operculina and other forms 

 of the Nimimidine type, its only point of accordance with OrbifoUtes or any member of the 

 MUioline type is the subdivision of its principal segments into sub-segments, and the multi- 

 plication of these upon a plan which is essentially cyclical. But the subdivision in question 

 is common, as we have seen, to all the principal types of Foraminifera ; and we have already 

 seen it presented in the Niniimidine series by Heferoster/iiia, the relation of whose chamberlets is 

 exactly the same as that which exists in Cycloclypeus. The affinity between these two forms, 

 in fact, is as intimate as that between Orbiculina and OrbifoUtes (^^ 143, 183), and is of 

 precisely the same nature ; for peripheral fragments of these two organisms could not be 

 distinguished from each other ; and the tendency of the later stages of growth in 

 Hefcrosfecjina, as in Orbiatfina, is to a change in the mode of increase, by the lateral 

 extension of the growing margin, from the spiral to the cyclical. 



501. Geographical and Geological Distribution. — We have at present no knowledge of the 

 present existence of Cgcloclj/pci/s in any other locality than that already mentioned (^ 493) ; 

 and no other examples of it have yet been discovered in a fossil state than those stated by 

 Mr. Carter (xxiii a) to occur in company with Orbiluides and Heferosfet/ina, on the south-east 

 coast of Arabia, in a white limestone apparently belonging to the early Tertiary epoch. 

 The structure of one of Prof. Ehrenberg's " casts " (Plate XXII, fig. 5) is in every 

 respect so conformable to that which would be presented by the body of Cgcloclj/peus, in 

 regard to the communications between the segments and the interseptal system of canals (as 



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