EXDOCEEATID^. 
139 
as to justify their incorporation with it. The descriptions of 
“ 0. duplex ” have often been based upon imperfect fragments, con- 
sisting of casts, or even of sections only, of a few of the chambers, in 
which the distinguishing characters are necessarily reduced to a 
minimum. In some instances the siphuncle only has been figured. 
In such circumstances I cannot vouch for the accuracy of all the 
references given above. The dubious ones are indicated by a note 
of interrogation. 
Amongst the specimens of E. Wcihlenhergi in the lluseum Col- 
lection from 'U^estrogothia two attain a considerable size, the longest 
measuring I foot 7 1 inches, the diameter at the larger end being 2^ 
inches and at the smaller end 10 lines. The other measures 1 foot 
5 inches in length, with a diameter of 2 inches and 8 lines at the 
larger extremity and 14 lines at the smaller, where it is broken, the 
chambers being here filled with coarsely crystalline calcite (fig. 14, «). 
A marble slab from Sweden contains a section of an Endoceras in 
which a portion of the body-chamber is preserved. This individual 
measures 2 feet 7:j inches in length and increases very slowly in 
diameter, measuring only 1 line at the apical and 1 inch at the basal 
extremity. On the whole it would seem to belong to a more slender 
and slowly tapering species than E. Waldenhergi. 
It is difficult to conceive how shells of such great length and 
thinness of texture could have been preserved from fracture even 
during the lifetime of the animal. Professor IVhitfield, of Now 
York, who has had exceptional opportunities of studying the shells 
of Endoceras in the rich deposits of the Trenton Limestone, as well 
as in the splendid collection 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 with- 
in the siphuncle served to protect that part of the body of the animal 
which extended back into it in a “ long finger-like projection.” 
The sheaths, he adds, “ were not only formed in case of accidents 
already having taken place, but were probably often formed to guard 
against future troubles ; consequently 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 crystalline 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 Pro- 
fessor Whitfield observes that in the American species he can “ find 
