BEEKMANTOWN AND CHAZY FORMATIONS OF CHAMPLAIN BASIN 4/5 



Aphetoceras attenuatum Hyatt 



Lituites farnsworthi Billings (pars). Pal. Foss. 1861. 1 :2i 

 Aphetoceras attenuatum Hyatt. Am. Phil. Soc. Proc. 1893. 

 32:449 



The original description of this species is : 



This species is founded upon the specimen described by Billings 

 on page 21 of his Paleozoic Fossils as having first two whorls in 

 •contact and making a coil an inch across. These whorls are, how- 

 ever, not in contact on his specimen, if my drawing of this is cor- 

 rect. The specimen is of nearly the same size as the type of Aphe- 

 toceras farnsworthi, but one and a quarter volutions are 

 free, so as to leave a gap of 8 mm before the completion of the first 

 quarter of the septate part of the eccentric volution, and at the end 

 of the same this gap has increased to 13 mm, and in the next quarter, 

 at the end of the living chamber, it is 25 mm. The departure of 

 the free whorl of farnsworthi increases, as shown in Billings's 

 drawing, in less than one half of a volution to 40 mm. 



The septate part of the eccentric volution in this specimen is 

 58 mm long, the living chamber is 88 mm long. The former would 

 occupy about three fourths of a volution if it followed a regular 

 open spiral curve, and the latter would be about one half of a volu- 

 tion, estimated in the same way. 



The septa are similar to those of farnsworthi. The frag- 

 ment of the siphuncle observable in the neanic stage changes in the 

 length of 10 mm from nearly subventran to propioventran. 



Position and locality. Beekmantown formation at Philipsburg, 

 Missisquoi co. 



Family trocholitidae 

 Genus schroederoceras Hyatt 



This genus has been separated by Hyatt [1894, p. 458] from Dis- 

 coceras, because the latter as defined by Schroder and Remele 

 has been used for the smooth forms, having a tetragonal section 

 of the whorl and a dorsal siphuncle, as well as for the costated shells. 

 These smooth shells have in the neanic stage decided costation with 

 the same aspect and contour as in the adult of the genotype of Dis- 

 eoceras ( D . antiquissimum). But as Hyatt holds : " Simi- 

 lar species having costations throughout life can not be included in the 

 same genus with those that have them only in the neanic and earlier 

 stages of growth " and he adds that " the large number and great 

 variety of form of these smooth species, while still maintaining this 

 difference of the later stages of growth, shows that this separation 

 indicates a natural distinction ". 



The species here described, would, as far as shown by material 

 we have had opportunity to study, seem to be entirely smooth in all 

 stages. 



