PLATE XIII. 



The figures in this Plate represeut various forms of the RotaUne tvpe, and illustrate tbe structure of AmpMstegina. 



Pig. 

 1.- 



2.. 

 3. 



4.- 



5.- 

 6.- 



v.- 

 8. 



9. 

 10.- 



n.- 



13.- 

 13- 

 14.- 



15.- 

 16.- 



17.- 



18.- 

 19. 



-Portion of the shell of an Acervuline Planorbu- 

 lina, much enlarged, as seen at a in its super- 

 ficial aspect, and at b in vertical section. 

 (After Schultze.) 



-Discorbina vestcularis, seen on its upper side. 



-The same, as seen on its lower side. 



-Pulvinulina vermlculata, seen on its upper side ; 

 at a is shown a small portion more enlarged 

 (seen as an opaque object), showing its granular 

 surface. 



-The same, as seen on its under surface. 



-Portions of the under surface enlarged, showing 

 at a its large orbuline pores, and at b its 

 minute tubuli arranged in clusters. 



-Rutalia Schroeteriana, viewed obliquely. 



-Transverse section of the same ; a, bifurcation 

 of the canals. 



-Vertical section of the same. 



-Side view of Cijmbalopora [Rosallna) Poeiji. 



-Basal view of the same. 



-Basal view of another specimen of the same. 



-Planorhullna vulyaris, as seen on its attached side. 



-Portion of the margin of the same, much more 

 enlarged, showing the communication of the 

 chambers by the apertural neclis a, a. 



-Portion of the free surface of tropical variety of 

 Planorbulina vulgaris, showing its prominent 

 tubercles. 



-PateUina corriigata, as seen from its upper sur- 

 face, showing a central and circumambient 

 chamber resembling that of Orbilolites, sur- 

 rounded by annular rows of chamlierlcts. 



-The same viewed from the under side, showing 

 the prolongation of the chamberlets towards 

 the centre, and the filling-up of the umbilical 

 cavity by a secondary growth. 



-Pohjtrema rubra ; a, globular form ; b, arbores- 

 cent form. 



—Portions of its surface more enlarged ; a, porous 

 areolae bounded by solid shell-substance ; b, 

 openings of large canals at the ends of the 

 branches. 



Fig. 

 20.- 



21.- 

 22.- 



23.- 

 24.- 



25. 



26.- 



28.— 



29.- 



Sections of the same, showing at a, a, large 

 canals formed by the coalescence of cham- 

 berlets, and at b, b, solid columns formed by 

 the deposit of calcareous matter in excess. 



Calcarina calcar. (After D'Orbigny.) 



Upper surface of Amphlsteginn mamniUlata. 

 (After D'Orbigny.) 



Lower surface of the same. 



End view of the same, showing the mouth, and 

 the superficial granular deposit in its neigh- 

 bourhood. 



Horizontal section of Amphisiegina, showing the 

 disposition of the chambers, the singleness of 

 the septa, and the tuberculated surface of the 

 septal planes and of the external surface of 

 the penultimate whorl ; a, small portion more 

 enlarged, to show the free openings of the 

 tubuli on the internal surface of the chambers. 



-Vertical scctiou of the same ; showing at a a, 

 the alar lobes of the upper surface, and at 

 a' a the alar lobes of the lower surface ; 



b, b' , the upper and lower umbilical bosses ; 



c, c\ c', c^, non-tubular portion of the spiral 

 lamina at the margin of the successive con- 

 volutions ; d, d' , thin cliamber-wall of the 

 last convolution ; e, e', thickened chamber- 

 wall of penultimate convolution ; /, the 

 aperture ; g, h, line marking the declination 

 of the spire ; i, apparent subdivision of the 

 outer wall of the convolution, resulting from 

 the backward elougation of the chambers. 



-Cast of the interior of Amphistegina, showing 

 the disposition of the alar prolongations of 

 the upper side. 



Cast of the interior of AmpMstegina, showing 

 the nearly complete detaclimenc of the alar 

 prolongations on the under side from the 

 principal segments, with which they are only 

 connected by the narrow necks a, a, and their 

 intercalation as " astral lobes." 



Cast of the interior of Amphistegina, showing a 

 subdivision of the alar lubes of the upper side 

 by incomplete partitions. 



