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apex as the grinding plane passed inwards. Fig. 20, same showing the metane- 

 pionic and paranepionic, both with dorsal furrows opposed to each other. Fig. 

 21, section of ana- and paranepionic volutions. This cut passed in the plane of 

 the first septum, truncating the fundus of this and then obliquely across the suture 

 line of the fourth septum. The second suture has a well-defined annular lobe and 

 cone. 



Figs. 22—27. Cymatoceras {Naut?)deslongchampsianum (sp. D'Orb.); Rouen; 

 Coll. Boucault and Bronn; Mus. Comp. Zool; Cretaceous. Figs. 22 and 23, side 

 and front views, natural size, nepionic stage and ananeanic substage (this shell 

 has faint longitudinal ridges and transverse bands on the casts not shown in any 

 drawings) the sutures and small umbilical perforations are shown. Fig. 24 

 shows metanepionic outline at second septum and paranepionic between the fifth 

 and sixth septum of the same specimen, both with dorsal furrows. Fig. 25, the 

 reverse of the same specimen. Figs. 24 and 26, part of cast of chambers in the 

 dorsal furrow of Fig. 24, showing the annular lobes. Fig. 27, another specimen 

 showing ananepionic substage at the first septum with a dorsal furrow, and para- 

 nepionic also with dorsal furrow between fifth and sixth septa. 



Fig. 28. Cymatoceras (Naict.) simplex (?); Yeoville, England; Coll. De Kon- 

 inck, Mus. Comp. Zool.; Cretaceous ; showing the nepionic volution and part of 

 the neanic stage. The slight subangular, umbilical shoulders which begin to 

 appear in the anephebic substage. The longitudinal ridges and transverse bands 

 are absent on this cast, but this may be due to the state of preservation. 



Figs. 29 and 30. Cymatoceras {Naut.} radiatum (sp. Sow.); Rouen; Boucault 

 Coll., Mus. Comp. Zool.; Craie Chlorite. Natural size. Fig. 29, side view show- 

 ing the fourth and subsequent sutures with the broad bands and constrictions 

 beginning in the ananeanic substage. In this the eighth and ninth sutures show 

 closer approximation than any of the preceding. Fig. 30 shows the same with 

 the ananepionic substage at the first septum and the paranepionic at the fifth. 

 The dorsal furrow begins immediately between the first and second septum in 

 the metanepionic substage as is shown by the cast of umbilical perforation and 

 by Fig. 1, PI. xiii. 



Fig. 31. Cenoceras granulosus, showing the ana- and metanepionic substages 

 with fragment of the dorsal shell and septa of the ananeanic whorl clinging to the 

 venter indicating the amount of involution and the depth of the contact zone. 



