BEEKMANTOWN AND CHAZY FORMATIONS OF CHAMPLAIN BASIN 503 



striction just posteriorly of the aperture, which is 

 produced by a ringlike thickening of the apertural tudinaf sSn 

 margin. Also two parallel vertical carinae of un- 



must be assigned to a genus with more primitive characters than 

 Gomphoceras has ; and is evidently a member of Hyatt's genus 

 Cyclostomiceras. 



The hyponomic sinus is shallow and narrow, 

 and situated opposite to the marginal, tubular, nar- 

 row siphuncle. The slight contraction of the living 

 chamber is largely due to a thickening of the shell 

 in apertural direction [see text fig. 57], evidently a 

 gerontic feature. On casts of the living chamber 

 one observes as in C . cassinense a deep con- Fi &- 57 cj cl °- 



minimum 

 Whitf. (sp.) 

 Part of longi- 

 tudinal section 

 showing thick- 

 ening of shell 



equal strength may be seen passing along the si- ?J?e nd \ 3 aper ~ 

 phuncular side of the cast. 



The species has not yet been observed outside of the beds at Fort 

 Cassin. 



Genus oncoceras Hall emend. Hyatt 

 Oncoceras pristinum sp. nov. 



Plate 34, figure i, 2 



Description. Small, very breviconic cyrtoceracone, which is 

 but slightly curved, the arc described by the outer margin having a 

 hight of 7 mm, when the length of the conch is 30 mm ; compressed, 

 the dorsal side rounder than the ventral ; the greatest diameter — 

 which is the dorsoventral one, at about the first half of the living 

 chamber — is 18 mm, the transverse diameter at the same place is 

 about 14 mm. The living chamber slightly and gradually con- 

 tracting in the last half ; not quite occupying one half of the conch. 

 Aperture apparently not contracted. Cameras shallow, 9 within the 

 space of 10 mm in the ephebic part of the conch; the septa but little 

 concave, their depth being about equal to that of one chamber, 

 rising toward the outer side of the conch. Siphuncle very slightly 

 nummuloidal, 1 mm wide, marginal at the outer side of the conch, 

 without deposits. Surface smooth. 



Position and locality. Of quite frequent occurrence in C 6 

 (Strephochetus bed) at Chazy village, but not observed in other 

 parts of the section at Chazy village. Also obtained by Prof, 

 van Ingen in three specimens from the Chazy beds in the Saranac 

 river at Plattsburg. 



Observations. We arc not aware of any eyrtoceracones 

 hitherto described from the Chazy rocks of New York or Canada, 

 with which this one could be compared, none of the others being 



