480 



NEW YORK STATE MUSEUM 



the transverse, depressed, elliptic section of the whorl throughout 

 life and the development of the siphuncle which becomes rapidly 

 propiodorsan. 



" The sutures of the earlier stages, which are straight are trocho- 

 litean in aspect, with well marked dorsal lobes, as is also the form 

 and ornamentation of the young whorls, which are slightly costated.'* 

 In the adult stage the sutures (of the fourth whorl) are stated to 

 have well marked lateral lobes and dorsal lobes in the contact 

 furrow. 



The tendency of the last whorl to become free, described by Whit- 

 field, has not been observed by Hyatt, the contact furrow being well 

 defined at the termination of the whorls of Whitfield's type. 



Genus deltoceras Hyatt 



This genus has been erected by Hyatt for several species from 

 the Quebec group (Beekmantown) of Newfoundland, only one of 

 which has thus far been described. It is stated to be represented by 

 shells similar to Aphetoceras but just one grade more complicated. 

 The whorls are compressed in section, the dorsum wider than the 

 venter, and the dorsoventral diameter much larger than the trans- 

 verse one, in both genera, but in this one they grow more rapidly in 

 ventrodorsal direction. The whorls are in contact, but no impressed 

 zone has been found at any stage and the gerontic or sometimes the 

 entire ephebic stage is free. In the neanic stage the sutures have 

 ventral and dorsal saddles and broad lateral lobes and in the ephebic 

 and gerontic stages, slight ventral lobes. The siphuncle is stated to 

 be in some species very large and ventral. All or nearly all of these 

 features will be found to be typically represented in the species from 

 the Champlain basin here described. 



Deltoceras vaningeni sp. nov. 



Plates 25-28 



Description. Gyroceracone of about three volutions wdiich 

 are in contact, without, however, developing an impressed zone ; only 

 the greater portion of the gerontic living chamber departing gradu- 

 ally from the coil. Rate of growth considerable, the conch increas- 

 ing its diameter about 23^ times within the last volution and attain- 

 ing a total diameter of 165 mm where the volutions are still con- 

 tiguous. Whorls subcircular, the ventral side a little narrower than 

 the dorsal one and becoming strongly flattened on the gerontic whorl, 

 while the dorsal side remains round and gibbous. No impressed 

 zone present. 



