EXPLANATION OE THE PLATES. 
37 
PLATE II. 
Fig. 1. Side view of a characteristic specimen of Peneroplis : — 1 a, front view, or septal 
plane, of the same, showing its single row of isolated pores : 40 diam. 
Fig. 2. Front view of a yoimg specimen, intermediate in its characters between Pene- 
raplis and Dendritina : — 40 diam. 
Fig. 3. Side view of a specimen of Peneroplis, of which the later chambers are widely 
extending themselves laterally : — 40 diam. 
Fig. 4. Septal plane of cyhndrical prolongation of Spirolina (see fig. 11), showing trans- 
ition between the isolated pores of Penevoplis and the coalesced fissures of 
Dendritina: — 40 diam. 
Fig. 5. Side view of a specimen oi Peneroplis, of which the later chambers are extending 
themselves longitudinally : — 40 diam. 
Fig. 6. Front view of a young specimen, intermediate in its characters between Pene- 
roplis and Dendritina : — 40 diam. 
Fig. 7. Side ■view of a specimen of Peneroplis^ of which the later chambers are extending 
themselves longitudinally, and of which the spu'e is more turgid, and the pores 
arranged in a double row, as shown at 7 : 40 diam. 
Figs. 8, 9, 10. Front views of young specimens of Peneroplis, showing various departures 
Lorn the normal type in the form of the septal plane and the disposition of 
the apertures : — 40 diam. 
Fig. 11. Side \iew of Spirolina, which bears the like relation to the Dendritina-i^^e 
shown in figs. 12 and 13, that the specimens represented in figs. 6 and 7 bear 
to the ordinary Peneroplis-ij^o ; the septal plane of its cylindrical extension, 
with apertures of intermediate form between those of Pmeroplis and of Den- 
dritina, is shown at 11 a : — 40 diam. 
Fig. 12. Side \T.ew of a tj’pical specimen of Dendritina : — at 12 a is shown the septal 
plane and single large dendritic orifice of its last chamber, and at 12 5 the 
same, from the preceding whorl ; al, al, alar prolongations of the chambers, 
which bear a much larger proportion to the principal cavity in the middle than 
in the later part of the growth : — 40 diam. 
Fio". 13. Side view of a specimen of Dendritina tending towards the Spirolina-ij^o, the 
last turn of the spire having already detached itself, and the last chamber 
ha\ing completely lost its alar prolongations, as seen at 13 a: — 40 diam. 
Fig. 14. Front view of a young specimen of Peneroplis, presenting a very marked 
departure from the ordinary type in the form of its septal plane and the 
disposition of its apertm’es : — 40 diam. 
Fig. 15. Septal plane of a specimen resembling in general form that represented in 
fig. 13, but showing a want of coalescence of the fissures of which the den- 
dritic orifice is made up : the ridge-and-furrow arrangement of the walls of 
