BEEKMANTOWN AND CHAZY FORMATIONS OF CHAMPLAIN BASIN 485 



gin by almost the length of the dorsoventral diameter, sides of aper- 

 ture with low crests. Cameras very shallow, the middle depth of 

 the cameras being 4 mm, where the volution has a diameter of 21 

 mm ; 7 mm where the diameter is 34 mm ; sutures nearly straight 

 in the early volutions, but developing a high ventral saddle and 

 shallower lateral lobes upon the later whorls. Septa deep, their 

 depth being equal to that of one chamber in the second whorl and 

 equal to that of two chambers in the third whorl. 



Siphuncle large (about one sixth of the diameter), tubular, propio- 

 ventran from an early stage onward. 



The surface of the first volution 

 marked with strong growth lines ; on the 

 second volution appear rounded costae, 

 which pass the sides very obliquely, 

 swinging backward from the line of in- 

 volution toward the abdomen. Where 

 the dorsoventral diameter of the whorl 

 is 35 mm, the distance of the crests of 

 the costae is 10 mm. Both the costae 

 and the concave interspaces bear a sys- 

 tem of strong raised lines, running par- 

 allel to the costae. 



Position and localities. Not uncom- 

 mon in the lower Chazy (bed B 4 )of the 

 Valcour section. Billings's original came 

 from the Chazy limestone of the Mingan island 

 the " Calciferous of the Mingan islands " and states that there are 

 similar forms in the same horizon in Newfoundland. Whiteaves has 

 lately [1903, p. 120] remarked that Hyatt was in error in placing 

 the species m the Beekmantown formation. Raymond [1902, p. 20] 

 cites a " L i t u i t e s undatus (?)" from the Chazy beds with 

 Maclurea magna at Crown Point, which presumably is a rep- 

 resentative of this species. 1 



Observations. Since neither Billings nor Hyatt has figured 

 this species and the latter author gives but a short note about the 

 form, identification of our material with the Mingan form had to 

 rest primarily upon a comparison with the original description and 

 it can not be overlooked that in such a proceeding important dif- 

 ferences may fail to be recognized. A comparison of our drawings 

 with authentic Canadian material in the museum at ( >ttawa has 



F igr. 44 Plectoceras jason 

 Bill, (sp.) Secdon or first 

 whorls, x V, 



Hyatt cites it from 



1 Mr Raymond informs me that the specimen is a small weathered frag- 

 ment. 



