305 



rib-like folds and raised lines of growth that cross the outer volution, both 

 of which are nearly straight on the dorsum, curved obliquely and convexly 

 backward on each side, and deeply and concavely sinuate on the venter. 



In a large number of specimens there is some diversity in the mode of 

 coiling, and in the surface ornamentation. The volutions are always 

 rather closely coiled, but they may be either separate but closely conti- 

 guous throughout, or partly in contact and partly free. In some specimens 

 the volutions are most distant posteriorly, and in others anteriorly. But, 

 in any case, there is no impressed zone or contact furrow on the dorsum. 



On the outer volution, the oblique, rib-like folds are most prominent 

 in the ventral and ventrolateral region, but in some large specimens from 

 Lorette there is a narrow, shallow longitudinal depression in the median 

 line of the venter, upon which some of these ribs or folds are more or less 

 obsolete. And, as before stated, in the small specimen from Watertown 

 that Hall figures as " Lituites undatus," the whole of the flattened venter 

 is practically smooth. 'J'he sutural lines of the Lorette specimens are 

 nearly straight, and the siphuncle is cylindrical, ventral and marginal. 



In the Museum of the Survey there are specimens of Plectoceras Halli 

 from the following localities in the Province of Quebec. Falls of the St. 

 Charles River, Indian Lorette ; collected by Logan and Richardson in 

 1852, by Ami and Giroux in 1888, and by Weston in 1898. St. Ambroise, 

 four miles north of Indian Lorette ; and Lac Oureau river (the Naque- 

 reau river of the " Geology of Canada ") above the mouth of the Rivifere 

 Rouge and S. W. of Joliette; collected by Logan and Richardson in 1852. 

 Also, three miles west of Napierville, south of Montreal, collector and 

 date not stated. From Ontario, a few specimens of P. Halli have recently 

 been collected at two localities near Ottawa by Walter R. Billings and J. 

 E. Narraway. 



By one alias or another, thi^ species has long been regarded as a cha- 

 racteristic fossil of the Black River limestone of the State of New York 

 by Emmons and Hall, and of the Province of Quebec by E. Billings and 

 Foord. But, it is to be noted that the limestone at the falls of the St. 

 Charles River, Lorette, where it is most abundant, was said to be of Tren- 

 ton age by Bigsby and Salter in 1853, and by Ells in 1888, though Ells 

 says that the beds at the foot of the fall " have a Black River facies in 

 their lowest portion.'' 



(3.) Plectoceras (?) undatum, Conrad. (Sp.) 



Plate 37. The only figure. 



IiMchui undatus (para) Conrad 1842. In Emmons' Geo). New York, Pt. II, 



Surv. Second Geol. Distr., p. 394, no. 104, 

 fig. 1. 



