128 FAMILY MILIOLIDA. 



comparison can the mutual relations of these be discovered ; and it will be desirable, instead of 

 commencing with the complex organism on which the genus was originally established, to 

 examine in the first instance those simpler or more elementary forms which afford the clue to 

 the interpretation of its character. For each of the principal modifications I am about to 

 describe, I shall adopt the distinctive name assigned to it by Messrs. Parker and Rupert Jones ; 

 but these names are to be understood as used merely for the sake of convenient identification, 

 and not as intended to indicate a definite boundary between the forms the}^ respectively desig- 

 nate, — no such boundary having, in our opinion, a real existence. 



189. In the East Indian and other tropical seas, generally adherent to the surface of 

 large, foliated, bivalve shells, such as Chama or Hippopus, but occasionally free in shell-sands, 

 the simple pupoid forms represented in Plate X, figs. 1 — 7, are not uncommon. Each of these 

 is composed of a linearly-arranged series of chambers entirely disconnected from each other ; 

 the external walls of these chambers and their dividing septa are very thick, and are 

 composed of porcellanous shell-substance exactly resembling that of the higher types of 

 Foraminifera with which we have been last engaged ; and their surface sometimes exhibits 

 minute pits, resembling those which we have seen to be common on the exterior of many of 

 the porcellanous series. Although the succession of these chambers is sometimes almost 

 rectilinear, it is generally more or less curved ; and the curvature is sometimes so great 

 that the series forms a half ring. Every chamber opens separately by a single large pore on 

 the middle of the concave side ; and this pore is surrounded, as in Pe/ieroplis, Orhitolites, &c., 

 by a prominent annulus of shell, which is sometimes so thick and large as to form a nipple- 

 shaped protuberance. The number of chambers is extremely variable, and is obviously depen- 

 dent upon successional growth. Although specimens are occasionally met with in which the 

 surface is smooth or nearly so, it much more commonly presents a strongly marked alternation 

 of ridges and furrows (figs. 3, 7), the former corresponding with the interseptal spaces, and the 

 latter with the septa ; there are instances, however, in which the interseptal spaces are depressed, 

 as in fig. 8, instead of being elevated. It now and then happens that the chambers are piled one 

 on the other, so as to form part of a double series (fig. 6). The length of any series will, of 

 course, depend upon the number of chambers which it contains ; the breadth of these bodies 

 usually varies between '007 and 012 incli. Tlie simple structure of this organism is diagram- 

 matically represented, as shown by horizontal and vertical sections, in Fig. XXV. Its mode of 



growth would be not a little perplexing, if we did not bear 

 Fig. XXV. in mind what has been already stated as to the extension of 



the sarcode-bod}' over the exterior of the shells of Forami- 

 nifera (^ 33), and the formation of new envelopes by portions 

 of that body protruded from the aperture (^ 31). It has 



been shown to be probable, in the case both of Orhitolites 

 Diagrammatic Sections of Dactylopora -, ^i t •• •/• ii-ii\i 



m,«:-A, horizontal; e, vertical. ^nd AheoJina, that (at certam tmies, if not habitually) the 



pseudopodial extensions from the separate pores coalesce with 

 each other on the exterior of the aperture ; and there is no more difficulty in understanding 

 how, from such a coalesced stolon of sarcode, a new chamber may be added to either extre- 

 mity of the linear series, or may be built (so to speak) as part of a new storey above it, than 

 there is in accounting for the formation of such a chamber in direct continuity with the aper- 



