On Cycloloculina. 537 



sufficient to disclose their identity with the smooth and regular 

 specimens which possibly represent individuals which had lived in 

 deeper and more undisturbed water, or under conditions less 

 favourable for exuberance of shell growth. 



A series of radial crinkles or undulations, which are more 

 noticeable in the thin- walled specimens than in the coarser shells, 

 might at first sight give the impression that the annular chambers 

 are divided by radial partitions into small chamberlets ; but 

 these markings are purely superficial, and the examination of 

 numerous balsam specimens has proved that the tubular chambers 

 are undivided throughout (plate XII. fig. 5). 



Mode of Growth. — The initial or " Discorbine " stage commences 

 with a primordial chamber, which is followed by about six other 

 chambers, crescentiform in shape, and arranged as in Discorbina 

 biconcava (Parker and Jones), to which species the shell, at the 

 completion of its first stage, bears some resemblance (plate XII. 

 fig. 1). With the seventh chamber, the second, or "Pavonine," 

 stage may be said to commence. Owing to its great breadth, as 

 compared with its diameter, it commences that overlapping of the 

 preceding chambers, which, continually increasing in the eighth 

 and ninth chambers, usually reaches its culminating point in 

 the tenth chamber, which completely infolds all its predecessors, 

 its opposite extremities meeting at the base of the shell. The test, 

 which had been more or less fan-shaped, or, rather, Pavonine 

 (peacock-tail shape) at the eighth and ninth chambers, is now 

 practically circular, only a slight flattening at the base showing 

 where the encircling edges of the tenth chamber have met (plate 

 XII. fig. 2). 



The third, or " Annular " stage of growth, now begins, and the 

 animal adds several tube-like undivided chambers, each of which 

 completely surrounds, all its predecessors (plate XII. figs. 3, 4). 

 The number of these chambers varies considerably. The largest 

 specimen which we have found shows six of these concentric 

 annular chambers. The specimen is imperfect, but it probably 

 marks the approximate limit of growth, as the average number of 

 annular chambers in the third stage does not exceed four. 



From the ninth or tenth chamber to the completion of the 

 shell, there is but little variation in the diameter of the tube-like 

 chambers, the average diameter of the chambers being about 

 * 05 mm. This means that the tubes, though very nearly circular 

 in section, are rather broader than they are deep. 



In the next species, however — Cycloloculina polygyra — the 

 variation is in the other direction, the depth being, if anything, 

 greater than the breadth. 



One abnormal specimen was found in which /the shell showed 

 signs of fracture and repair during the third stage of the animal's 

 life. A considerable piece of the test has been broken away, 



