132 
NAUTILOIDEA. 
which are not very numerous, and occur at irregular intervals (fig. 
13). An endosiphon^ is present, hut it is rarely preserved (fig. 13). 
receives strong support from the structures observed in Endoceras helemniti- 
forme. He further observes that in the forms [of the Cephalopoda] having 
a small siphuncle, that organ is in a retrograde condition. 
It may be interesting to notice, before quitting the subject of the embryonic 
condition of the shell in Endoceras, that Barrande described a fossil, which was 
collected at Pbillipsburgh, in the Eastern Townships of Canada, in the lime- 
stone of the Quebec Croup (Upper Cambrian or Lower Ordovician). This 
fossil he took to be “ the initial part of the shell of an Endoceras,'' and gave it 
the name of Endoceras Marconi. The figures of this fossil give one the 
impression that it is a portion of the siphuncle, because it is marked by a series 
of obhque rings, which are acutely bent upwards on one side, just as in fig. 10 , 1 
{ante, p. 129). The dark space represented in the cross sections I should judge 
to be one of the sheaths which occupy the cavity of the siphuncle in this genus. 
E. Marconi is described in Barrande’s Syst. Sil. de la Boheme, vol. ii. Texte iii. 
1874, p. 748, and figured on plate ccccxxxi. ff. 11-15, and plate cccclxxxviii.. 
Case vii. 
^ This term was first made use of by Prof. Hyatt {loc. cit. p. 201 ), who 
discovered the endosiphon in the present genus, and recognized its similarity to 
the central slender tube already well known to palaeontologists in Actinoceras. 
Exception might perhaps be taken to the word “ endosiphon ” on the ground 
that it seems to imply the existence of two siphuncles, an inner and an outer 
one. It will be found convenient, nevertheless, to designate what is doubtless 
the remains of the fleshy siphuncle (a diverticulum of the mantle) by some 
name which may serve to distinguish that organ from the shelly wall tliat 
separates it from the septal chambers. The term siphuncle having always been 
used in the latter sense, in relation to fossils, it would be difficult now to give 
it a wider signiflcation without causing confusion, and therefore I think the 
employment of the additional name is justifiable. 
Since Hyatt’s discovery of the endosiphon in Endoceras, Dr. Holm has also 
met with it in the same genus, and he describes it as a “ fine, cylindrical, 
tubular canal . . . surrounded by a very thin wall”(“Ueber einige bei 
dem Endoceren vom fleischigen Sipho im Siphonalrohre erzeugte Bildungen,” 
Palseont. Abhandl., Band iii. 1885, Heft i. p. 11). He refers to Barrande's 
figures of Endoceras insulare, Barr., in which the endosiphon is clearly depicted. 
This species was obtained from the Ordovician rocks of the western coast of 
Newfoundland, near the French fisheries. It is figured in the Syst. Sil. de la 
Boheme, vol. ii. 1870, pi. ccccxxx. ff. 5, 8, and pi. ccccxxxi. f. 8. 
Amongst the remarkable structures described in Endoceras helemnitiforme, 
there is one to which it seems desirable that I should revert ; this is the cal- 
careous deposit observed at the apical extremity of that species (see fig. 12 c, cd). 
Now as this appears to be strictly homologous with the conical deposit 
{calotte conique) described by Barrande in Orthoceras truncatum (ante, p. 23), it 
will be useful to consider here the more recent views put forward by Prof. 
Hyatt regarding the origin of such deposits (Proc. Amer. Assoc, for the 
Advancement of Science, 1883, vol. xxxii. p. 323). 
Prof. Hyatt’s opinion is expressed in the following passage {loc. cit. p. 336) : — 
“The truncated shells of Orthoceras have been described by Barrande; and 
