NAtlTILID^. 
57 
Sj). Char. Shell coiled and forming at least one volution and a 
half ; depressed vertically, so that the section is transversely ellip- 
tical, the ratio of the two diameters, augmenting gradually with age, 
is 24 : 32 in an adult specimen. A ridge, more prominent in adult 
than in young shells, is formed along the median line of the periphery. 
The sides are suhaugular, and have a waved outline imparted to 
them by the projection of the prominent nodes which ornament the 
surface of the shell and strongly mark even the cast. Septa 
moderately distant from each other, being 5 lines apart where the 
longer diameter of the shell is nearly 2J inches ; arching forward 
upon the periphery and forming a shallow sinus on either side of it, 
again inclining slightly forward at the lateral angles, and thence 
pursuing a straight course upon the concave aspect of the shell. 
The increase in diameter is in the ratio of 1 to 21 in a complete 
volution. The siphuncle is situated close to the convex border of 
the shell, in the median lino of the periphery ; it is cylindrical 
and of moderate size ; and sometimes contains radiating deposits. 
The ornaments of the test are very prominent : taking first those of 
the convex or outer aspect of the shell, they consist of nine or ten 
longitudinal ridges crossed by numerous fine and close-set imbri- 
cating striae, which give rise to slight nodes in crossing the ridges. 
In addition to these this region of the shell is furnished with 
“ three longitudinal rows of elevated tubercles, which are geminated 
or united together in pairs. The tubercles of the median row are 
placed a little behind those of the lateral rows, they are also less 
elevated, a little elongated, and arranged in a zigzag direction. 
In each pair placed on the side [the lateral angle], the tubercle 
which occupies the lateral keel is larger and more prominent than 
that of the back, to which it is joined by a sort of pinching up of 
the shell ” {(VArchiac de Vernueil). The tubercles are thus pro- 
duced by the crossing of the longitudinal and transverse ornaments. 
The large lateral tubercles or folds, which occur at pretty regular 
intervals (of about I inch), doubtless mark the position of successive 
apertures of the shell. The concave surface of the shell is orna- 
mented only with faint longitudinal ridges, crossed by the fine 
imbricating striae already described. The body-chamber in this 
species has not been seen. 
Remarks. Among the many figures given of this species, repre- 
senting it in various stages of growth and in different conditions of 
preservation, those of d’Archiac and de Vernueil, and of G. and F. 
Sandberger illustrate its characters most faithfully. It is difficult, 
without examining the original specimen, to estimate rightly the 
value of the claim put forward for regarding the Sjpirula nodosa of 
