303 



subquadrate, the ventral side being the broadest, as well as being consi- 

 derably flattened. The surface is ornamented with oblique, rounded, not 

 very prominent annulations, divided by concave interspaces of about 

 equal width. The annulations bend backward on the ventral side and 

 there form a deep sinus ; while on the dorsal or concave side, approach- 

 ing the umbilicus, they become quite obsolete ; the young shell is almost 

 smooth. The entire surface of the test is covered with very fine trans- 

 verse lines both on the ribs and the interspaces, and there are also obscure 

 traces of longitudinal lines. The septa are a little more than 1 line apart, 

 where the shell has a ventro-dorsal diameter of 6 lines. The siphuncle is 

 not seen." The species is said to be represented in the British Museum 

 collection by two specimens from the Black River limestone at Lorette, 

 and the specimen figured is not much more than two inches in its maxi- 

 mum diameter. These specimens are obviously those that Dr. Bigsby 

 collected at Indian Lorette in 1822, and that Salter referred to Lituites 

 undatus in 1853.* 



The specimen from Watertowa, N.Y., that Hall figures under the 

 name Lituites undatus and that Foord includes in his synonymy of Tro- 

 choceras Halli, is very little more than two inches and a quarter in its 

 greatest diameter. It is No. ^^^^' of the pal«ontological department of 

 the New York State Museum at Albany, and has been kindly lent to the 

 writer by Dr. John M. Clarke. It is obviously immature, as the earlier 

 volution and part of the later one are smooth, the oblique rib-like folds, 

 which are five in number on each side, being developed only on the outer 

 portion of the last volution. The venter is flattened and unusually 

 smooth, while the siphuncle is both marginal and ventral. It is most pro 

 bable that this specimen is the original of the smaller figure of Inachus 

 undatus, Conrad, in Emmons' report on the Geology of the Second Dis- 

 trict of the State of New York. 



In 1898 Mr. T. C.Weston visited Lorette, on behalf of this Survey, and 

 succeeded in collecting for its Museum a fine series of unusually large and 

 well preserved specimens, that agree very well with Foord's descriptions 

 of Trochoceras Halli, but that give some additional information in regard 

 to its characters. These specimens have been described, and their generic 

 and specific relations discussed in some detail, in two papers, the one entitled 

 "Notes on some Canadian specimens of ^Lituites undatus,' and the other 

 "Additional Notes on some Canadian specimens of ' Lituites undatus,' " 

 published in the Ottawa Naturalist for October and December, 1 903. The 

 latest results of a study of these and other specimens are embodied in the 

 foregoing synonymy. It is now obvious that the Trochoceras Halli of 

 Foord is a Plectoceras closely allied to P. Jason (Billings) but apparently 



* In the Quarterly Journal of the Geological Society of London, vol. IX, p. 86. 



