PLATE XIX. 



Heterostegina and Cyclochjpeus. 



Fig. 



1. — Surface view of a full-grown specimen of Heteros- 

 tegina, showing its tendency to assume the 

 discoidal form by the opening out of the spire ; 

 a, b, c, thickened margin of the spire ; c, d, a, 

 its growing edge or septal plane : 10 diam. 



2. — General view of a disk of Cycloclypeus, showing 

 the aspect of its surface, and the appearances 

 presented by horizontal and vertical sections : 

 12 diam. 



3. — Vertical section of the shelly lamina enclosing 

 the chambers of Cycloclypeus, showing its 

 lamellated structure ; a, a, one of the cones 

 of non-tubular substance replacing the ordi- 

 nary tubular substance b, b, over the septa; 

 c, section of one of the interseptal canals : 150 

 diam. 



4. — Thin section of the same lamina taken parallel 

 to the surface of the disk, showing its mi- 

 nutely tubular structure, except where it over- 

 lies the annular septum a o ,■ at c c are seen 

 the divided ends of vertical branches of the 

 interseptal system of canals : 100 diam. 



5. — Ideal figure of a portion of a Cycloclypeus disk, 

 laid open to show the details of its structure ; 

 a, a, a, upper lamina, consisting of superim- 

 posed tubular lamellae ; b, b, b, lower stratum ; 

 c, c, c, cones of non-tubular substance, some- 

 times perforated by larger canals ; d, d, d, 

 their bases, forming tubercles on the surface ; 

 e, e, plates of non-tubular substance overlying 

 the septa ; /, /, passages of communication be- 

 tween the chambers through the inter-annular 

 partitions, as seen in section ; ff, g, the same, 

 as seen from the interior of the chambers ; 

 h, h, interseptal canals cut across ; ;, a chara- 



FlG. 



ber on the walls of which the system of in- 

 terseptal canals is represented as fully dis- 

 played ; k, k, passage of the principal canals 

 along the line of junction between the roof of 

 the chambers and the vertical septa: 60 diam. 

 6. — Diagram of a single chamber of Cycloclypeus, 

 showing its relations to other chambers and to 

 the interseptal system of canals ; a, cavity of 

 chamber ; b, b, adjacent chambers of the same 

 annulus, each separated from a by a double 

 septum ; c, c', and d, d' , chambers of external 

 and internal annuli, separated from a by the 

 partitions e c, e e , but communicating with it 

 by the passages/, /,/,/"; in the septa between 

 a and b, b, are seen the interseptal canals g, g, 

 each of which sends two oblique branches 

 across the annular septa, to communicate with 

 corresponding canals i, i in the septa dividing 

 c, c and d, d' ; these interseptal canals seem 

 to communicate by short, lateral twigs with 

 the cavities of the adjacent chambers, whilst 

 at g' g they become connected with vertical 

 branches, which unite them with those of other 

 planes ; at h, h, h' , h' are seen the canals 

 proper to the annular septa. 

 7. — Section of Cycloclypeus passing through its 

 median chambered plane, showing portions of 

 four annuli, 1 1, 2 2, 3 3, 4 4, with the general 

 relations of their chambers and their connec- 

 tion by the passages a b, a b, the double septa 

 by which they are separated, the thickening 

 of the annular partitions by intermediate de- 

 posit, and (in parts) the interseptal system of 

 canals : 36 diam. 



