604 MESSES. E. HEEON-ALLEN AND A. EAELAND ON THE 



what inflated terminal chamber. This figure does not appear to bear much external 

 resemblance to the original figure of either M. sollasi or 31. polita, although he suggests 

 that it is a specimen of the (hypothetical) initial spiral of the latter species. In the 

 Brady Collection at Cambridge a slide labelled " Peneroplis-Spirolina : P. cylindraceus 

 Lam., P. lituus Gmel.," contains the typical P. cylindraceus {Nautilus acicularis Batsch) 

 and specimens of Monalysidium ijolita Chapman. 



Oebitolites Lamarck. 



118. Orbitolites marginalis Lamarck. 



Orhulites marginalis Lamarck, 1816, etc., ASV. vol. ii. p. 196, no. 1*. 



Orbitolites marginalis Carpenter, 1856, etc., RF. 1856, p. 192, pi. ix. figs. 1-4 etc. 



Carpenter, 1883, EGO. p. 20, pi. iii. figs. 1-7 ; pi. iv. figs. 1-5. 

 „ „ Brady, 1884, FC. p. 214, pi. xv. figs. 1-5. 



„ Egger, 1893, FG. p. 248, pi. iii. figs. 46, 47. 



Chapman, 1900, FLF. p. 180, pi. xx. figs. 1-3. 



16 Stations. 



Universally distributed and often abundant, occasionally attaining exceptionally fine 

 proportions and growth, especially at Stns. 9 and '?X; most abundant at Stns. 1, 2 a, 

 and 9. 



The difficulty of separating this species from 0. duplex is often considerable, 

 especially in an advanced stage of growth. The typical features of 0. marginalis rest 

 upon the researches of Carpenter, and in a lesser degree of Brady, for the original 

 description of Lamarck, " Utrinque plana, margine porosa," is useless for purposes of 

 specific identification. The usual features associated with the species are the presence 

 of a pavonine initial series of chambers and a single marginal row of pores. 



0. duplex, on the other hand, is distinguished by a double row of marginal pores 

 and " a very slight approach to that orbiculine spire which is typical alike of 

 0. tenuissima and of 0. marginalis, approaching much more closely to the true cyclical 

 plan of 0. complanata. The nucleus [sic) consists, as in 0. marginalis, of a small 

 primordial chamber which is surrounded by a circumambient chamber; and round this 

 nucleus is seen a row of chamberlets which often at once forms a nearly entire 

 annulus, the ring being soon completed in succeeding circlets, and all subsequent 

 additions being made on the cyclical plan " (C, 1883, RGO. p. 26). Carpenter's word 

 " nucleus " refers, of course, only to the primordial chamber of the calcareous test, and 

 not to the true or protoplasmic nucleus. 



It appears, therefore, that Carpenter differentiates the two species as follows : — 

 0. marginalis. 0. duplex. 



Initial portion, orbiculine ; marginal 

 pores, single. 



Initial portion, milioline (cornuspirine) ; 

 marginal pores, double. 



* The geaeric name Orbitolites was instituted for 0. complanata and 0. concava in Lamarck's earlier 

 Systeme des Animaux sans Vertebres ' (Paris, 1802), p. 376. 



