ADDENDA. 381 



ORTHOCERAS MEDULLARE, p. 353. 



Since the preceding pages have been printed, a review of the descriptions 

 of Mr. M'Chesney, together with other information obtained, induces me 

 to believe that his species O. stricelineatuin is identical with O, viedullare. 

 The dates of publication of the species are respectively as follows : O. me' 

 dullare, Feb. 1860, and O. stricelineatum^ Feb. 1861. 



ORTHOCERAS SCAMMONI (M'CnESNEY). 



Two specimens, received from Prof. Marcy, offer some elucidation 

 of the characters of this species not before understood. A single 

 specimen combines in itself characters of O. columnare and O. scammoni ; 

 and unless we can jfind sufficient differences, on a further examination of 

 collections, to sustain the separation, the O. scammoni and others, as well 

 as that referred by me to O. angulatum^ will fall under O. columnare, 

 which has priority in time over those described by M'Chesney. The 

 cancellated figures 10 and 11 of Plate 19 (10) are apparently only the 

 well preserved impressions of the external surface markings of the same 

 species. It is probably also the same species which has been described by 

 Mr. Billings, in 1866, as Orthoceras cadmus. 



AMBONYCHIA ACUTIROSTRA, p. 336 (32). 



The citation from Greological Report of Wisconsin is an error. The name 

 there stands Amhonychia mytiloidea : the correction to A. acutirostra was 

 made in the proof, but seems to have been omitted by the printer, and I 

 have cited it from recollection; the species having remained thus labelled 

 in my collection for many years. Under this impression, I have cited 

 it without examination ; and I now find, on reference, that the fossil 

 published under the name A. mytiloides is the same. Since, however, this 

 name is preoccupied,* I propose to substitute A. acutirostra for the species, 

 which is now figured on Plate 15. The locality (Bridgeport) was erroneously 

 given in my paper. The original is from near Milwaukee ; but there is a 

 single specimen from Bridgeport in the collection of Prof. Marcy, which 

 appears to me identical with it. 



* Ambonychia mytiloides, Pal. N. Y., Vol. i, p. 315. 



