REPORT ON THE GENUS ORBITOLITES. 19 



having presented itself which did not bear some evidence of injury of this kind. 

 Where only small portions of the margin are broken away, the next-formed annuli extend 

 themselves along the fractured edge ; and thus the cyclical mode of growth is completely 

 maintained, with only a temporary irregularity: In PI. I. fig. 6, is shown a disk of 

 which more than one-half, together with the " nucleus," had been lost before the pro- 

 duction of the last two zones. These have not only been formed, as ordinarily, round 

 the unbroken margin, but have extended themselves along the fractured edge, and have 

 even filled up the space originally occupied by the " nucleus "; and the annuli being thus 

 completed, the disk will continue to grow on the cyclical plan, and even (as is shown in 

 the like examples of Orhitolites complanata, PI. VIII.) may recover in great degree its 

 circular shape. But qyqu a mere fragment broken away from the margin of a disk may 

 suffice to originate a new one, as shown in PL I. fig. 7 ; the form characteristic of 

 the type being completely restored. Owing to the transparence of this specimen, I have 

 been able to assure myself that every part of the margin of this fragment — whether 

 broken or unbroken, peripheral, central or lateral — has contributed to the formation of 

 the first new complete annulus, by which the foundation was laid of the subsequent 

 regular series of concentric zones ; thus clearly indicating that a sarcodic extension took 

 place from every chamberlet laid open by the fracture, as well as from the normal pores 

 of the last septal plane, and that these extensions coalesced to form a continuous ring, as 

 in the formation of the ordinary succession of concentric annulL It is most interesting 

 to observe that the zone of chamberlets to which this sarcodic ring gave origin is formed 

 upon the perfected type, without any reversion to the earlier " peneropline " stage. 



Geographical and Bathjmetrical Distribution. — So far as is at present known, 

 Orhitolites tenuissima inhabits only the North Atlantic Ocean and the seas in com- 

 munication with it. The first complete specimens of this type were obtained in the 

 " Porcupine" dredgings of 1869, at depths of from 630 to 1443 fathoms, between the 

 north-west of Ireland and Eockall Bank. In the " Porcupine " expedition of 1870, 

 however, it was brought up from a bottom of only 64 fathoms, in Setubal Bay on the 

 coast of Portugal, and afterwards from a shallow bottom within the Mediterranean, 

 near Carthagena. That it is an inhabitant of other parts of the Mediterranean I then 

 inferred from having detected fragments of it in the Foraminiferal dredgings made at 

 250 fathoms' depth by Prof. Edward Forbes and Lieut, (now Admiral) Spratt in the 

 .^gean, in 1842 ; and it is stated by the Eev. A. M. Norman, in Dr. J. Gwyn Jeffreys 's 

 Eeport on the " Valorous " cruise, that it has been dredged by the Marquis da Mon- 

 terosato, at from 100 to 200 fathoms' depth, off the coast of Sicdy. That it might 

 extend far to the north, would be expected from its capability of bearing the low tem- 

 perature of 37° Fahr., which prevails over the deep bottom from which it was first 

 brought up ; and this expectation was verified by its presenting itself in one of the 



