[Endoceras] duplex," Wahlenherg et aucit. 399 



more slender and slowly tapering species tkan E. Wahlen- 

 hergi. 



It is difficult to conceive how shells of such great length 

 and thinness of texture could have been preserved from frac* 

 ture even during the lifetime of the animal. Professor 

 Whitfield, of New York, who has had exceptional opportu- 

 nities of studying the shells of Endoceras in the rich deposits 

 of the Trenton Limestone, as well as in the splendid collec- 

 tions preserved in the American Museum of Natural History, 

 affirms that he finds them " nearly always in a fragmentary 

 condition, the earlier parts having been broken away or 

 otherwise destroyed ; " and he supposes that the sheaths 

 formed within the siphuncle served to protect that part of the 

 body ef the animal which extended back into it in a "long 

 linger-like projection." The sheaths, he adds, ^' v/ere not 

 only formed in case of accidents already having taken 

 place, but were probably often formed to guard against future 

 troubles; conseq^uently we sometimes find them crowded 

 together, so as to leave not more than an inch or so between 

 them, and the intervening space filled with coarsely crystal- 

 line calc-spar, showing that the one below had not been 

 injured so as to admit the access of foreign matter, which is 

 always sure to be the case where injury has occurred to the 

 individual sheath below the cavity so filled." 



With reference to the number and disposition of the sheaths 

 Professor Whitfield observes that in the American species he 

 can " find no regularity whatever in the distances at which 

 they occur even in the same individual. They often occur 

 quite close together, sometimes three or four of them being 

 ensheathed within each other ; and others again will have 

 from 10 to 20 inches between them ; and I have seen 

 examples of the shell from 2 to 4 fQot long without a trace 

 of a sheath " *. 



This species resembles in some respects, as in the distance 

 of the septa, and the proportionate size of the siphuncle, 

 Endoceras helemnitiforme^ Holm (Palaont. Abliandl. 1885, 

 Bd. 3, Heft i. p. 5) ; but in the latter the septa are said to be 

 equally distant from the very commencement of the shell, 

 which is not the case with the present species, in which the 

 septa are much closer together in the apical portion of the 

 shell than they are at later stages of its growth. 



The rare preservation of the apical end of these long and 

 finely pointed shells will always make any characters founded 

 upon the form of the apex but seldom available for purposes 



* Bull, American Mus. Is'at. Hist. no. 1, New York, Dec. 23, 1881 

 p. 20. 



