Beproductive Condition of Orhitolites, &g. By H. B. Brady. 695 



numerous sections I have made from them reveals a single such 

 embryo m sittL Be this as it may, it is quite safe to say that 

 specimens in the precise condition of those now brought under notice 

 are practically new to morphologists. 



The specimens obtained on the Suva reef vary a good deal as to 

 size and external characters ; the drawing, Plate X. fig. 1, represents 

 one of the larger and more characteristic of them. The dimensions 

 range from a diameter of about a quarter of an inch to very nearly an 

 inch (6 mm. to 24 or 25 mm.) ; but from the broken edges of the 

 smaller discs it may be inferred that they have lost some of their outer 

 annuli. At the centre, the disc is often not more than 1/300 of an 

 inch (0 • 08 mm.) in thickness, but this increases rapidly, though by no 

 means regularly, towards the circumference. The shells are seldom 

 so massively built as those in the ' Challenger ' collection or as others 

 which have come under my notice. The ' Challenger ' specimens, if 

 I understand rightly, were found unattached, in some of the more 

 sheltered pools on the reefs, and as they were taken at a different 

 season of the year (ui July) they may perhaps represent a later stage 

 in the history of the animal. 



The plication of the margin is also a very variable feature ; for 

 whilst some of the discs are very deeply lobed and divided, others, 

 generally those of smaller size, are only shghtly crenulated, and the 

 peripheral edge shows little tendency to duplication. The edges are 

 often ragged and grooved, owing to the breaking away of the external 

 annular septum, whilst the lateral walls are left standing. Wherever 

 the peripheral wall is fractured, the annular space it inclosed is seen to 

 be completely filled with young shells in the earhest stages of develop- 

 ment, as shown in fig. 2. These, however, are not confined to the 

 outermost circlet. If a horizontal section of the disc be made no 

 less than five or six of the outer annuh may often be found more 

 or less closely packed with these little bodies (fig. 3). It was 

 previously known that the later chambers of this variety of Orbitolites 

 were not regularly subdivided into chamberlets on the normal plan,* 

 but the explanation which could only be conjectured is now obvious. 



The embryo shells correspond exactly with what is termed by 

 Carpenter the " primitive disc " or " nucleus " of the typical Orbitolites 

 comjolanafa. They are compressed discs generally rounded, often 

 nearly circular, in outline, but sometimes sHghtly irregular, or even 

 subangular (figs. 4 -7). Their diameter ranges from 1/60 to 1/30 in. 

 (0-4 mm. to 0*8 mm.), their thickness averaging about 1/100 in. 

 (0 • 25 mm.). The lateral surfaces are flat or somewhat convex, seldom 

 perfectly even, but more frequently marked by slight irregular eleva- 

 tions and depressions (figs. 4, 5). The peripheral edge is rounded 

 and presents either one or two rows of perforations placed at tolerably 

 regular intervals on a slightly elevated ridge (figs. 6, 7). The orifices 

 are sometimes situated in small nipple-like protuberances. The 



* This is well shown in the drawing of a transverse section in the ' Eeport on 

 the Challenger Foiaminifera,' pi. xvi., fig. 11, 



3 B 2 



