PLATE YII. 



PeneropHs, with its Dendritine and Spiroline varieties. 



Fig. 

 1.- 



3.— 



6.- 



11.- 



12.— 



Ideal figure of the Dendritine variety of Pene- 

 ropHs, partly laid open, so as to show the 

 arrangement of its chambers, the nature of 

 their communieation by a single fissure of irre- 

 gular form (simpler in the earlier whorls, or 

 even replaced by a set of multiple pores), the 

 investment of the earlier whorls by the alar 

 prolongations of the chambers of the later, and 

 the detachment of the last convolution from 

 the preceding. 



Portion of the surface of a specimen of Pene- 

 ropHs on which the plications are obsolete, 

 but the punctations are arranged in rows cor- 

 responding to them iu distance : 100 diam. 



Portion of the surface of a specimen of PeneropHs 

 over which the punctations are scattered with- 

 out definite arrangement: 100 diam. 



-Lateral view of Spiroline variety of PeneropHs ; 

 at a is seen the septal plane of its rectilineal 

 extension : 40 diam. 



-Septal plane of another SpiroHne form, showing 

 a transition between the isolated pores of 

 PeneropHs and the coalesced fissures of Den- 

 dritina ; 40 diam. 



-Lateral view of a young specimen of PeneropHs, 

 showing the greater turgidity of the spire and 

 the greater breadth of the septal plane (a) in 

 that stage, with a coiTCspouding ari'angement 

 of the multiple pores: 40 diam. 



10. — Front views of young specimens of Pene- 

 ropHs, showing various departures fiom the 

 normal type in the form of the septal plane 

 and the disposition of the multiple pores : 

 40 diam. 



-Lateral view of a young specimen of PeneropHs, 

 showing in the disposition of the apertures of 

 its septal plane (a) a tendency towards the 

 Dendritine variety : 40 diam. 



Lateral view of a specimen of PeneropHs, of whicli 

 the later growth is rectilineal, as in the Spiroline 

 variety, but of which the form is compressed 

 and the pores quite distinct from each other, 

 though arranged in a double row, as seen at 

 a : 40 diam. 



Fig. 

 13- 



14.— 



-Lateral view of a typical specimen of the Den- 

 dritine variety : 40 diam. 



15.- 



IG.- 



17.- 



18.- 



19.— 



20.- 



21.— 



Septal planes of the same — a, from the Ia.st 

 chamber ; b, from the preceding whorl ; c, 

 from an earlier whorl, — showing the progressive 

 increase in the complexity of the dendritic 

 aperture; al, at, alar prolongations of the 

 chambers of the earlier convolutions : 40 

 diam. 



Septal plane of a specimen resembling in general 

 form that represented in Pig. 13, but showing 

 a want of coalescence of the fissures of which 

 the dendritic orifice is made up ; the ridge- 

 and-furrow arrangement of the walls of the 

 chambers is here prolonged in an unusual 

 manner over the borders of the septal plane : 

 100 diam. 



Lateral view of a typical specimen of PeneropHs ; 

 at a is seen its long, narrow, septal plane, with 

 a single row of isolated pores arranged at 

 pretty regular intervals : 40 diam. 



Front view of a Dendritine variety of peculiarly 

 turgid form, showing the lateral extension of 

 its aperture in accordance with the shape of 

 its septal plane : 40 diam. 



Ideal figure of PeneropHs, partly laid open, so as 

 to show the arrangement of its chambers, the 

 nature of their communications by isolated 

 pores, and the difi'crcnces in the arrangement 

 of these in the earlier and in the later convo- 

 lutions, iu accordance with the form of the 

 septal plane. 



Front view of a Dendritine variety of peculiarly 

 compressed form, showing the narrowing of 

 its aperture in accordance with the shape of 

 its septal plane : 40 diam. 



Portion of the ordinary surface of PeneropHs, 

 showing its ridge-and-furrow plication and its 

 rows of minute punctations : 100 diam. 



Portion of the ordinary surface of a Dendritina, 

 showing precisely similar characters : 100 

 diam. 



