﻿565 



upon the edge of the aperture or rather in the base of the dorsal 

 crest. The aperture had the usual shelf-like constriction figured 

 by Meek and on the dorsal side were two narrow sinuses and a 

 median dorsal crest, the length of which could not be determined. 



Mr. Stanton, in his " Colorado Formation,"* shows a similar re- 

 tention of the impressed zone in Scaphites ventricosus. 



The gerontic whorl is quite free for some distance, and although 

 the impressed zone sensibly diminishes in depth and breadth 

 towards the aperture it is not obliterated. These two species have 

 comparatively short living chambers, which are free only for a part 

 of their length, and one would naturally expect that the very deep 

 contact furrow of the ephebic and anagerontic substage would per- 

 sist. The conditions are quite different from those that occur in 

 shells with more extended gerontic stages, like Scaphites larvce- 

 f or mis, Meek and Hayden, and in these the paragerontic substage 

 may perhaps have no impressed zone. 



I have, however, examined a considerable number of scaphitoid 

 shells from European localities and some of these gave positive 

 information of the persistence of the impressed zone in the lower, 

 inner border of the aperture, although, as in Scaphites nodosus, it 

 was sometimes hardly perceptible in the outline of this part. 



Helicancylidce. 



This family name serves the purpose of temporarily uniting all 

 phylogerontic species of the Cretaceous in America which have 

 three rows of tubercles on either side. The characteristics are 

 given below under the generic title " Helicancylus. " 



Helicancylus, Gabb.f 



It is probable that genetic connection as shown by the ornamen- 

 tation existed between cretacic shells of normal involute form like 

 Acanthoceras Remondi of the nodose variety figured by Gabb as 

 having three rows of tubercles and his Crioccras latus % This last 

 also has three rows of spines and single costae, but has an open coil 

 without an impressed zone. There are similar marks of affinity in 

 the species described by the same author as Helicancylus cequicosta- 

 tus, which has also three rows of nodes. The last, however, lias the 



*Bull. U. S. Gcol. Survey, Pis. xliv and xlv. 

 fPal. Cal, i, PI. xiii, and ii, PI. xxv. 

 J Ibid, i, PI. xv, Fig. 2. 



