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widely separated and are inclined apically and the sides flatter. 

 This difference in the inclination of the ribs shows that the slight 

 crest in the lines of growth and probably apertures of the ephebic 

 stage have been lost in the gerontic stage. 



The dorsum as the bend is made becomes flattened and when 

 this is completed it is a distinct furrow which cannot be called a 

 dorsal furrow or a contact furrow. The true dorsal furrow, if it 

 occurred at all in this form, must have been between the protoconch 

 and the apex, the true contact furrow probably did occur in the 

 nepionic stage which has not yet been seen. 



This furrow then which occurs in the bend before the contact of 

 the gerontic volution or arm takes place is probably a gerontic 

 dorsal furrow. The lines of growth in this furrow are bent for- 

 wards into a slight but well-defined crest in two of the specimens 

 examined and the costations were wholly absent. The umbilical 

 perforation which occurs here is not very small and it occurs be- 

 tween two straight volutions and is the reverse morphically of the 

 nepionic perforations ; thus it also is a gerontic perforation and 

 not an umbilical perforation, a degenerative and not a progressive 

 character. The length of this perforation was 4 mm. more or less 

 in three specimens ; the vertical diameter was very much less but 

 was not measurable. 



Just before contact takes place one costation crosses the dorsum 

 with a forward bend or crest in two specimens. Close to it, but 

 at the contact, in another specimen, there occurs a costation which 

 is the reverse of this, having a sinus which marks the beginning of 

 the gerontic contact furrow. This furrow in the only fragment 

 showing the dorsum in older parts of the gerontic stage obliterates 

 the costse. The lines of growth were nowhere visible in this con- 

 tact furrow, so that, whether this side had crests or sinuses in the 

 apertures, could not be observed. 



Ptychoceras TexanuxM, Shum.* 

 Loc, Chatfield, Texas. 



Three fragments of this species, sent like others through the kind- 

 ness of Mr. T. W. Stanton, show peculiarities with reference to the 

 gerontic contact furrow and gerontic dorsal furrow, resembling 

 essentially those described for Ptychoceras crassum, but in this 



* Identified by Mr. T. W. Stanton. See Shum., Proc. Bost. Soc. Nat. Hist, viii, p. 190. 



