FOURTH, OR I ORONU EB \N BRANCH. 168 



In other young specimens, the acutenesa of the abdomen begins upon the latter 



of tin' third or firs! part of the fourth whorl, and tin- striae of growth are 



a- and well marked. Previous t<> this the abdomen is rounded, as in 



/ ' 



The smoothness of the siil<-^ of the whorls, the immature folds, and the flat 



lal aspecl of the young, make the Bhell very like /■ /• <. and 



in the next the folds L r i\c an aspect s •what similar to the pUeahu 



The prolonged smooth stage of the young, before it 

 takes on the folds, has do correspondence with any form of Caloceras, and 

 indicates direct derivation from pianorbe, var. leve. In the typical specimens 

 it. acutuhraale, the folds are sometimes nol apparent upon 

 tin- cast, even upon the fifth whorl, but in one specimen a careful exarai- 

 i showed that tin- original Bhell must have had faintly marked folds, 

 which stretched entirely across tin- Bide and bad tin- usual abrupt terminations. 

 Quenstedt 1 tiirur. •-< this variety. The aperture is shown in hi- Fig 27 to have 

 been similar to that of pianorbe, having a well marked rostrum, broad lateral 

 sinuses, ami a constriction. It is by no means certain, as Quenstedt states in 

 the same work on page 104, that Wright's figure of the young of sermeostatum, 

 Plate I Fig 7 of his "Lias Ammonites," i- a specimen of this Bpecies; it is 

 quite as likely that Wright was correct. Professor Quenstedt' a specimens at 

 TQbingen are for tin- most part young from the Oelschiefer, but a large one 1 

 ■arl\. if not quite, full grown. Tin' keel in this appeared as a sharp 

 mil maintained tin- Bame character in adults. 

 The abdomen does not broaden out as in adult of acuiidorsale, hut per- 

 u maintaining it- angular character throughout life. The piloe 

 quite early, hut never appeared to get beyond the fold-like Btage. Some- 

 times, however, they bend forwards and maj cross t I « « - abdomen, and thru the 

 abdominal ridge forming tin- keel is crenulated.' The variety occurs in South 

 1 ally in the Oelschiefer of Quenstedt 



■ rtn doubtfully referred to this variety was collected by Professoi Orton 

 at Ipisbguaniina in Northern Peru.* 



\ w; cuneiforms 



I'Ulr II. i i K . :. 



II l \ l : . I 



i variety I irlj convex ; pilao 



most prominent in the centre, ami sloping gradually to either side. 



I lominal lobe is somewhat longer than the two lateral lobes, which 



: perior lateral lobes and Baddies are pointed, the 



inferior lateral lobes and saddles mere 

 often »fT- 



