REPORT ON THE GENUS ORBITOLITES. & 



Hu united Quoy and Gaimard's recent Marginopoya (as I had myself previously done) 

 with Lamarck's fossil OrhitoUtes ; but so little did he know of the internal structure of 

 this type, that he altogether failed to perceive its very close similarity to that of 

 Orbiculina, which he ranked with Peneroplis, Dendritina, and other genera allied to these, 

 among his " Helicostegues." 



This similarity had been already recognised (1850) byPi'of. W. C. Williamson, whose 

 previous studies of Foraminiferal structure had so far pre^aarcd him for the right apprecia- 

 tion of it, that, on coming into possession of specimens of OrhitoUtes may-ginalls^ from 

 the calcareous sands of Havannah, and of a small worn specimen of the recent OrhitoUtes 

 complanata from Tonga, he made it perfectly clear, by a comparison of their internal 

 structure with that of the proteiform OrhicuUna adunca, that these three types closely 

 accord in their general structure, differing only in their plan of growth (Transactions of 

 Microscopical Society, vol. iii., 1852). And it is greatly to his credit, that at a time when 

 the authority of M. d'Orbigny was generally accepted as the highest in regard to 

 Foraminifera, Prof. Williamson should have ventured not merely to call in question the 

 A'alue of " plan of growth " as an ordinal character, but even to rank it as good only for 

 speciJiG differentiation. He clearly showed (l) that the well-known Orhicidina adunca 

 of the Antilles, though always beginning life as a HeUcostegue, often ends it as a 

 Cyclostegue ; its first-formed arcuate rows of chamberlets, which represent the successive 

 chambers of the flattened spire oi Penero2)Us, often sending backwards two alar extensions, 

 which meet at the back of the first-formed spire, so as to form a complete annulus, after 

 which every successive addition takes place on the cyclical plan; (2) that whilst in OrhitoUtes 

 marginalis the first growth is spiral, yet this very early gives place to the cyclical 

 plan ; and (3) that in OrhitoUtes complanata the growth is cyclical from the beginning, 

 the very first row of chamberlets forming a comjalete annulus, and all further additions 

 being made on the same plan. He also showed that OrhitoUtes marginalis and OrhitoUtes 

 complanata alike originate in a globular or pyriform primordial chaml)er, which opens 

 by a flask-shaped neck into a second chamber ; and that it is from the latter that the 

 first row of chamberlets originates in each case. He fully recognised also the " sim- 

 plicity " of the structure of OrhitoUtes marginalis, with its single tier of chamberlets, and 

 the " complexity " of that of OrhitoUtes coinplanata, with its " multiplication of strictly 

 analogous parts "; and he showed that the latter is further differentiated by its possession 

 of concentric rows of supevficial fossse, distinct from the cavities of the intermediate 

 stratum of the disk. And the only considerable error in his whole description, which 

 arose from the abrasion of the surface of his single specimen of the " complex " type, was 

 his treating the chamberlets of the superficial plane, which are closed-in by lamellae of 

 shell, as open fossse. The great importance, then, of Prof. Williamson's memoir, lay in 



' It is unfortunate that Prof. Williamson misnamed the specimens he so well described. His Orbindina complanata 

 is clearly the OrhitoUtes marginalis of Lamarck ; while his Orbiculina tonga is no less clearly the Marginopora vertebralis 

 of Quoy and Gaimard, the recent type of Lamarck's fossil Orbitolites complanata. 



