io8 THE FORAMINIFERA 



peneropline and orbiculine arrangements have entirely gone in 

 the megalospheric form. 



We turn now to the other species, commonly included in the 

 genus Orbitolites, the 0. tenuissima of Carpenter (Figs. 39 and 40). 



The tests are exceedingly thin (-^-5-5- inch), though they may 

 attain 30 mm. in diameter. 



FIG. 39. 

 Orlitolites tenuissima, Carp. The complete test, x about 11, from a photograph. 



There are undoubtedly points of similarity in structure be- 

 tween this species and 0. marginalis, the simplest of the other 

 members of the genus. The annular arrangement succeeds a 

 spiral one, and the annuli are divided into chamberlets by septa 

 disposed in a manner which is very similar to that found in 0. 

 marginalis, especially in examples from deep water in which the 

 radial septa are sometimes incompletely developed. Coming to 

 the middle of the test, however, we find ourselves in new country. 

 In five specimens a globular central chamber about 31 /z in 

 diameter * occupies the centre, and leading from this is a succession 



1 In that figured in Plate I. Fig. 1 of Carpenter's Report the central part of the 

 test appears to have been left blank, without any intention of depicting a central 

 chamber of the size of the blank space. The specimen here figured was obtained by 

 the Travailleur in the Bay of Biscay, and I am indebted to the authorities of the 

 British Museum for the opportunity of giving a photograph of it. The central 

 chamber measures 30 x 31 p.. In the four other specimens in which I have been able 

 to obtain evidence of the size of the central chamber, it appears to be about the 

 same. 



