UPPER TRIASSIG SPECIES. 119 



The specimen does not give a very clear idea of the details of the 

 septa ; but, as nearly as they can be made out, they seem to present the fol- 

 lowing- characters: siphonal lobe narrow, oblong, and apparently merely 

 provided with two small, short, simple, terminal divisions, as in T. Whitneyi. 

 The sinus on each side of this is smoothly rounded, and about as wide as 

 long, while the first lateral lobe is smaller, and also shorter than the siphonal 

 lobe, and armed with a few digitations at the end. Between the latter and 

 the umbilicus, there are two shallow, smoothly-rounded sinuses, and two 

 small lobes, the first of which seems to be digitate at the end and the other 

 smooth. 



Locality and position. — Same as last. 



-AKOESTID^. 



"Genus ARCESTES, Suess. 



'■^Ammonites (sp.), Munster, Klipsteiu, Hauer, Giebel, Quensteclt, and others; notBrug. 



as restricted. 

 "Arcestes, Suess (1865), Akad.'d. Wissensch., LII, 76. 



"The genus Arcestes of Suess, like Phylloceras and Lytoceras of the same 

 author, is a well-defined generic group. I have been justly criticised by 

 Dr. Laube for unintentionally omitting, in my preliminary essay on the 

 'Fossil Cephalopods of the Museum of Comparative Zoology' at Cam- 

 bridge, to give credit to Prof Edward Suess for having been the first to 

 suggest, in any published communication, that the Ammonites were suscep- 

 tible of generic subdivision. I was, however, unacquainted at that time 

 with Professor Suess's results, and therefore must still continue to attribute, 

 so far as I am concerned, the credit of the idea to Professor Agassiz, who 

 gave me the information long before Professor Suess had published his 

 paper.* 



"Other criticisms with which I have been favored will be best answered 

 by the memoirs now in course of publication at the Museum of Comparative 



* It is well known to the writer, and many others in this country, that Professor 

 Hyatt had long been at work on his subdivisions of the Ammonites before the publi- 

 cation of Professor Suess' paper; though no one will i>retend to qiiestion the fact that 

 Professor Suess' conclusions were independently formed, and have priority of publica- 

 tion.— F. B. M. 



