538 Transactions of the Society. 



and the gap filled up, not by the restoration of the broken annular 



chambers, but by the insertion of irregular chaniberlets, which fill 

 the space and complete the circular outline of the shell. 



The species varies considerably in size, but the following 

 measurements may be taken as approximating to an average of 

 the various stages : — " Discorbine " stage : length, • 26 mm. ; 

 breadth, ■ 20 mm. " Pavonine " stage : length, ■ 5 mm. ; breadth, 

 0*6 mm. Adult, or "'Annular" stage: diameter, 1-1*1 mm. 

 The concentric annuli average ■ 05 mm. in diameter. 



The thickness of the specimens is approximately the same in 

 all stages of growth after the first few chambers, and an average 

 for a moderately flat specimen would be ■ 046 mm. 



Cycloloeuliaa polygyra sp. n. Plate XII. fig. 8. 



Definition of Species. — Test free, complanate, discoidal, con- 

 sisting of the three series of chambers arranged symmetrically in one 

 plane. Peripheral edge nearly square. Perforations finer than in 

 the type, and without any secondary deposit of shell substance 

 between the pores. Sutural lines either very slightly depressed, 

 or flush, or even slightly limbate. Number of chambers in the 

 first two stages, usually eight. Average number of chambers in 

 the third, or " Annular " stage, about five. The annular chambers 

 increase regularly in diameter, instead of remaining of practically 

 constant diameter, as in C. annulata, and this gradual increase 

 gives a false impression of a closely coiled spiral, whence our 

 specific name ''polygyra." As the thickness of the test is prac- 

 tically the same in all stages, it follows that the internal section 

 of the chambers varies at different stages of growth, the early 

 chambers being almost ribbon-like, while the later ones are 

 nearly square in section. 



The species is founded on certain specimens which are found 

 associated with* C. annulata in several of the gatherings. It is of 

 very infrequent occurrence as compared with the type, and all the 

 specimens hitherto found are adults. There is, however, no doubt 

 from their structure, that the test passes through the same three 

 stages as does C. annulata, from which it differs in several essential 

 features. 



The chief differences are : — 



A. In size, the species is considerably smaller than C. annulata. 

 Our largest specimen of C. polygyra measures ■ 5-0 ■ 6 mm. in 

 diameter, which is less than the average size of C. annulata. The 

 shell is altogether smaller, neater, and more finished in appearance 

 than the type. 



B. The peripheral edge is square, not rounded, as in C. annulata, 

 and the sutural lines are only slightly depressed, and sometimes 

 flush or limbate. 



