98 



W. B. CARPENTER ON THE STRUCTURE OF ORBITOLITE8. 



of Ireland, some extremely thin Orbitoline disks were obtained, 

 about the size of a fourpenny piece. Although they were nearly all 

 broken, it was very interesting to find them presenting unmistakable 

 evidence of a Milioline origin. I have thus been able to trace 

 the development of the Orbitoline type along a series of forms, 

 beginning with the simple undivided Cornuspira, a flat shell very 

 like a Peneroplis, but without any division into chambers; the 



%6 



Fig. 10. 

 Structure of Shelly Disk of Orbitolites complanata, 



1. Edge of disk, showing multiple series of marginal pores. 



2. Vertical section, showing two superficial planes of chamberlets, sepa- 

 rated by intermediate columnar structure. 



3. Internal Structure : — a, superficial chamberlets ; b b, columnar 

 chamberlets of intermediate layer ; c, floors of superficial chamberlets, 

 showing the opening at each end into the annular gallery beneath; d, 

 annular galleries cut transversely; d' d", annular galleries laid open longi- 

 tudinally; e e,ff, oblique stolon passages intermediate layer. 



