3.38 
XAUTILOTDEA. 
the suture line above mentioned, and helps to produce the swollen 
band or collar at this point (fig. 72, c). This porous layer had, 
according to Barrande \ a very wide superficial extension. That 
Tig. 73. 
Atnria. At uri — Enlarged representation of part of two of the invaginated septal 
necks, broken o]ten, showing the different layers of which the siphnncle is 
composed, a, fold, where the new 7ieck (invaginated within the preceding 
one) begins ; this fold marks the position of the suture line, desc*ribed else- 
where in the text ; h, h, nacreous layer of the older neck ; c, c, nacreous 
layer of the newer neck ; d, d, its commencement ; e,e, porous layer, which 
forms a lining between the nacreous layer h, b and/,/, the yellow layer 
(“ conche jaune” of Barrande), which covers the interior, and is regarded 
by Barrande as representing the corneous layer investing the fleshy 
siphuncle in the recent porous layer of newer neck. The 
projections h, h represent, approximately, the greatest expansion of the neck 
anteriorly ; i, i, broken line of the older neck ; X', continuation of the 
porous layer, showing its granular surface. 
“ cretacee”) (Extrait des Archiv. du Mus. d’Hist. Jsat., Paris, 1839, p. 306) ; and 
by the brothers Sandbei’ger as “ Sinterrohre ” (Die Yerstein. Nassau, 1852, 
p. 140). All these authors are referred to by Barrande, who translates their 
observations (Syst. Sil. de la Boheme, vol. ii. pt. i. ; texte, pt. iv. 1877, p. 336). 
More recently, Mr. Henry Brooks has described the structure of the siphuncle 
and necks of jS\ pompilius, and found that the “ porous layer ” is composed of 
“ slender transparent sticks of calcareous matter ” .... “ held together in 
bundles by organic matter” (Proceed. Boston Soc. Nat. Hist. vol. xxiii. 1888, 
p. 380, pis. i., ii.). 
^ Syst. Sil. de la Boheme, vol. ii. pt. i. ; texte, pt. iv. 1877, chap, ix., “ Defl- 
nilion et structure du Siphon dans les Nautiiides,” pp. 341-346. 
