38 DE. CABPEXTEE'S EESEAECHES ON THE FOEAMINIFEEA. 



the chambers is here prolonged in an unusual manner over the borders of 



the septal plane: 100 diam. 

 Figs. 16, 17, 18, 19. Side and front views of young specimens of Peneroplis, showing 



various departures from the normal type in the form of the septal plane 



and in the disposition of the apertures : 40 diam. (See also figs. 2, 6, 8, 9, 



10, 14.) 

 Fig. 20. Portion of the ordinary surface of Peneroplis more highly magnified, showing 



its ridge-and-furrow plication, and its rows of minute punctations: 100 



diam. 

 Fig. 21. Portion of the ordinary surface of Dendritina, showing precisely similar 



characters: 100 diam. 

 Fig. 22. Septal plane of a specimen of Dendritina, showing the punctations continued 



over its surface: 100 diam. 

 Fig. 23. Portion of the surface of a specimen of Peneroplis, on which the plications had 



become obsolete, but the punctations are still arranged in rows corresponding 



to them in distance : 100 diam. 

 Fig. 24. Portion of the surface of a specimen of Peneroplis, over which the punctations 



are scattered without definite arrangement : 100 diam. 



PLATE III. 



Figs. 1-9. Side and front views of specimens of Operculina at various ages, showing 

 differences in the form and proportions of the spire, in the surface-markings, 

 and in the number and arrangement of the tubercles marking the septal 

 bands: 10 diam. 



Fig. 10. Hemispherical cluster of tubercles occupying the umbilicus of the variety of 

 Operculina represented in figs. 11, 12 : 25 diam. 



Figs. 11, 12. Side and front views of young and mature specimens of peculiar variety 

 of Operculina, characterized by the rapid opening-out of the spire, and by the 

 extraordinary development of tubercles, not only along, but also between the 

 septal bands: 10 diam. 



PLATE IV. 



Fig. 1. Part of the internal surface of one of the chambers of an Operculina that pre- 

 sented large tubercles on its exterior, showing the uniform distribution of the 

 tubuli except along the septal bands, and the comparatively large size of their 

 orifices : 120 diam. 



Fig. 2. Section through the wall of a contiguous chamber of the same, showing the 

 partial deficiency of tubuli in certain spots, with their crowding together in 



