536 Transactions of the Society. 



created to include those forms in which the test was discoidal 

 and composed of concentric segments, but in Orbitolites, and its 

 isomorph Cytloclypeus, these annular chambers are subdivided by 

 partitions into chamberlets, as is also the case in Orbiculiiw, which 

 in its variety compressa (0. comjjrrssa d'Orbigny), bears a remark- 

 able resemblance to our form. 



Terquem in his celebrated monograph * figures and describes 

 several abnormal Piano ■rbulince, most of which occur among the 

 Selsey fossils. One of his species, viz. Planorbulina Jiabellum 

 (Terquem),t bears a strong resemblance to the Pavonine stage of 

 Cycloloculina, and is indeed probably referable to this genus, 

 though apparently not to either of the Selsey types. Terquem's 

 figure differs from our form in the shape of the later chambers, 

 which are arcuate instead of being tubular and of horseshoe form. 



Terquem's figure does not, however, tally very accurately with 

 his description of the species, which is stated to be very variable 

 in shape and in the number of chambers. In this respect it differs 

 again from our form, in which the chambers are remarkably con- 

 stant in shape and nearly always ten in number, up to the comple- 

 tion of the Pavonine stage. 



Cycloloculina annulata sp. n. Plate XII. figs. 1-7. 



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

 ing of the three series of chambers arranged more or less irregularly 

 in one plane. Peripheral edges of the chambers rounded. The 

 entire surface of the shell, including the peripheral edge, some- 

 what coarsely perforate. No aperture to the test other than these 

 perforations, which represent the sole means of communication 

 between the successive chambers of the test. 



The surface of the test varies greatly in individual specimens. 

 It is occasionally almost smooth, clear, and distinctly hyaline, and 

 in these specimens, which are always regularly complanate, the 

 peculiar arrangement of the chambers is tolerably apparent even 

 when the shell is viewed as an opaque object, the concentric 

 sutural furrows being clearly marked. In the majority of specimens, 

 however, the test is irregularly complanate, and the surface is so 

 distorted by the irregular crenulated growth of the chambers, and 

 so roughened by the depositions of secondary shell deposit round 

 the edges of the perforations, that the sutural furrows are only 

 visible at intervals. The real structure of the test is thus masked, 

 and such specimens might easily be overlooked or regarded as 

 abnormal Planorbulincv of the " larvata " group. The transference 

 of these thick and coarsely built specimens to balsam is, however, 



* Les Foraminiferes do l'Eocene des Environs de Paris. By M. 0. Terquem, 

 Mem. Soc. Geol. de France, ser. 3, ii. (1882). 

 t Tom. cit., p. 92, pi. xi. fig. 19. 



