536 DE. CAEPENTEE'S EESEAECHES ON THE FOEAMINIFEBA. 



contigus, non apparens au-dehors, et rayonnee a 1'exterieur par des sillons ou des cotes 

 qui traversent la direction des tours. Ouverture composee de plusieurs trous diverse- 

 ment disposes." The genus was soon afterwards adopted by M. D'OBBIGNY in his first 

 systematic classification of Foraminifera * ; and he seems also to have adopted LAMARCK'S 

 idea of the structure of this type, which he defines as folloAVsf : "Les Polystomelles se 

 distinguent de tous les genres de Nautiloidees par ce caractere singulier, que les ouver- 

 tures du bord de la derniere loge reparaissent en fossettes, plus ou moins allongees, sur 

 toutes les autres; les dernieres seulement ouvertes, les autres fermees. II en resulte 

 qu'exterieurement ce genre se distingue de suite par . ce grand nombre de petits exca- 

 vations transversales, qu'on remarque sur toutes les especes." He elsewhere adds to 

 this description : " L'animal fait sortir des filamens non seulement par des ouvertures du 

 dessus de la derniere loge, mais encore par des pores des cotes des dernieres" J. The 

 same definition is more concisely repeated by M. D'OKBIGNY in his latest publication on 

 the subject, notwithstanding that the true structure of Polystomella crispa had in the 

 mean time been elucidated by Professor WILLIAMSON in his admirable memoir on that 

 species ; the genus Polystomella being still defined (in the ' Cours Elementaire de Pale- 

 ontologie et de Geologic Stratigraphiques,' torn. ii. p. 197) " Coquille nautiloide, pourvue 

 de nombreuses ouvertures sur la derniere loge et sur les cotes de la coquille ; une cavite 

 simple au loges." 



174. I have already referred, in my General Introduction, to the elaborate inquiry of 

 Professor WILLIAMSON into the organization of Polystomella crispa^, as having not only 

 established several important facts in regard to its minute structure, but as having fur- 

 nished the starting-point for all future investigations of the same kind : it now becomes 

 necessary that I should somewhat fully recapitulate the most important features of his 

 description, in order that it may be seen in what points my own inquiries upon a more 

 developed form of the same group have evolved results supplementary to his. To the 

 accuracy of his descriptions I can bear the fullest testimony ; having not only had the 

 opportunity, through the kindness of Professor WILLIAMSON, of examining the prepara- 

 tions still in his possession both of the shell and of the animal of Polystomella crispa, 

 but having carried out an independent investigation upon specimens collected by 

 myself. 



175. On the exterior of each of the segmental divisions of the shell of P. crispa, strong 

 transverse crenulations present themselves, which are deepest near the convex margin of 

 the preceding septal band, where they terminate somewhat abruptly, and usually dis- 

 appear before reaching the concave margin of the subsequently-formed chamber. The 

 depressions between the elevated ridges, which are the " fossettes " of M. D'ORBIGNY, 

 often present the appearance of orifices; but this appearance is fallacious, since at no 



* "Tableau Methodique de la Classe des Cephalopodes," in Anuales des Sciences Naturelles, 1826. 



t Voyage dans I'Amerique Meridionale, torn. v. p. 29. 



J Foraminiferes Fossiles de Vienna, p. 121. 



Transactions of the Microscopical Society, First Series, vol. ii. p. 159. 



