— 347 — 



ed in a spécimen of P. Mansuyi {vide infra), but in tliat 

 shell the pariétal barriers of the older séries were tiie 

 fîrst to be absorbed and of the later séries to first to be 

 formed. In that case, moreover, the two sets were not 

 superimposed but nearly 1/4 of a whorl distant. 



The only other variation in the armature I was able 

 to observe in the spécimens of P. Giardi opened was in 

 the anterior pariétal plate, which in some cases was 

 longer than in the type, reachiug close up to the horizontal 

 fold above it. Of the larger spécimens, one with the parié- 

 tal ridge at the aperture only just commenced, showed 

 some déviation from the normal armature. The anterior 

 pariétal vertical plate was found to be triangularly dilated 





Fig. !• Fig. Ib 



at its lower extremity, buti do not attach much impor- 

 tance to this feature. A more striking différence was 

 seen in the palatal barriers ; the second and third folds 

 having the vertical portions very short, while their upper 

 anterior and lower posterior horizontal portions are consi- 

 derably elongated ; the fourth, on the other hand, bas the 

 vertical portion more elongated, being nearly twice as long 

 as the fifth and threetimes the length of the third ; the 

 fifth fold is normal, but the sixth is more elongated though 

 less elevated and nearer the lower suture than in the type. 

 Between the posterior terminations of the second and 

 third folds occurs a low denticle not observable in the 

 type (see fig. 1^). 



