296 FAMILY NUMMULINIDA. 



in consequence of their following a somewhat oblique direction. Still their continuity 

 is maintained through all the successive layers of which even the thickest part of the 

 shelly disk may be composed, and they open upon the surface along the borders of the 

 septal bands or spots of non-tubular shell-substance (fig. 5, e, e). The annular system 

 of canals traverses the thick band of shell-substance that usually intervenes between 

 the successive annuli, and is continually brought into view in horizontal sections 

 (fig. 6, h li, Ii! H). It appears from vertical sections traversing the annular septa, that 

 several tiers of these annular canals may exist. I have frequently ti'aced them running con- 

 tinuously for a considerable distance, without appearing either to give off any branches, or 

 to communicate with the radial canals ; but I have occasionally seen appearances which 

 indicate that such a communication is estabhshed by means of canals passing vertically 

 downwards at the angles of the chambers, so as to unite the three sets of canals into one 

 continuous system, furnished with a multitude of orifices upon tlje surface of the disk. A 

 representation of the whole canal-system, as I believe it to exist in this organism, is given 

 in fig. 5. 



499. Monstrosities. — Although the number of specimens of this type which I have had 

 the opportunity of examining is but small, yet two among them exhibited the same kind of 

 monstrosity as that which is common in Orhitolites ; namely, the superposition of a vertical 

 plate upon the horizontal disk (If 181). And in each it is sufiiciently apparent that this 

 plate has originated from the central cell, and that its increase has taken place pari i)assu 

 with that of the horizontal disk. 



500. AJfmiiies. — There cannot be a better case than that which is afforded by the type 

 under consideration, for testing the relative values of a classification based upon plan of 

 yrowtk, and of one based upon the internal structure of the sJiell, as affording the key to the 

 natural affinities of an organism for which a place has to be assigned ; and it will, therefore, 

 be worth while here to review the principal facts relating to the structure of Cycloclypeus, and 

 to compare them with those furnished by Orbitolitcs and its allies on the one hand, and by 

 Ninnmulina and other members of the Nummuline series on the other. The sole point of 

 resemblance between Ci/clocli/pci(s and Orltitolites consists in this — that the mode of growth 

 is cyclical, the extension of the disk being effected by the formation of successive annuli, 

 each of which is divided by radiating partitions into secondary chamberlets. But it has been 

 shown that the lateral communication between the chamberlets of each annulus of the simple 

 type of Orbitolitcs is so free, that the sub-segments of the animal body which occupy them 

 are simply beaded enlargements of the continuous annular stolon that constitutes the 

 principal segment ; and that it is from the intermediate portions of that stolon, not from the 

 sub-segments, that the radiating extensions issue which go to form a new annulus. In 

 Cyclochjpeus, on the other hand, the chamberlets of each annulus are completely cut off from 

 direct communication with each other laterally, opening only into the chamberlets which lie 

 next them in the central and pei'ipheral directions ; so that the adjacent sub-segments forming 

 each annulus have no mutual connection, and their extension in a radial direction by means 

 of the extensions they put forth will take place with entire independence, except as regards 

 the coalescence of these radiating stolons after they have issued from the marginal pores. 



