36 G. LINDSTRÖM, THE ASCOCERATIDAE AND THE LITUITIDAE. 
portionally with the other specimens. The body chamber ends as a truncated cone, obliquely 
on the side of the central axis of the shell near the convex side and in some specimens 
close to it. 
As a series of specimens can be followed from the smaller and more regular to the 
larger and more deviating or having the true Ascoceratid characters, it will be best to 
begin the description of the former as probably representing the earliest stage of deve- 
lopment. In pl. VII fig. I we see the smallest specimen, 45 millim. long by 15 millim. 
broad, with a length of the body chamber of 33 millim. There are four extremely thin septa, 
deeply funnel shaped, having a difference of 13 millim. between their bottom and their 
uppermost edges. Near the concave side they are parallel or regularly distantiated from 
each other with 3 millim., in the bottom or lowest down they are widest apart with 5 
millim. and on the convex side they approach near to each other with a curvature, as close 
as one millim. and again at the edges they are as much distantiated as on the other side 
or even a little more owing to their ascending steeper there than on the other side. 
Around the siphonal aperture the bottom of the septum is elevated and the neck is curved 
downwards and backwards, as to resemble a hook when seen in a section (Pl. VI fig. 
10 a). In the older septa a spur has grown out from this hook toward the centrum 
through which the aperture of the siphuncele has been contracted. This progressive growth 
is of use when the shell is ready to decollate a part of itself, as will be seen further on. 
The elements of the siphuncle are in the youngest specimens nearly cylindrical, only a 
little swollen in the middle, 53 millim. in length and 3 millim. in breadth. 
Next in size and further development we have the specimens delineated in pl. VII 
Jigs. 4—8. In figs. 7 and & the siphunele already approaches to the bulbous form, its ele- 
ments having both diameters alike. In fig. 4 likewise, though the bulbous character there 
is more prominent. The shape and the position of the septa, which in all seem to be four, 
is quite the same as in the youngest form. In fig. 12 there is a decided change to the 
nummuloid shape, the diameters being 3 and 5 millim., but still four septa. In fig. 3 a 
most remarkable specimen is represented. It is larger than any of the preceding, has 
four regular septa and a fifth incomplete one. This specimen thus leads us from the first 
mentioned specimens to those which have three or more incomplete septa. This adventive 
septum is quite regular on the concave side of the shell and has a lacune in its middle 
on the convex side and is consequently only visible near its upper and lower end in a 
section going through the centrum. The elements of the siphuncle are decidedly nummu- 
loid, the first having 3 millim. in height and 5 in breadth, the following decreasing a 
little till the fourth which has 2: 5. The necks of the septa are hooklike and re- 
curved and more strongly developed than the other. From this transitory or intermediate 
specimen we pass to those which may be regarded as the oldest (Pl. VI f. 10—19, pl. 
VII f. 1—2). Here we find commonly only three complete septa and three incomplete, 
making six in all. Their obliquity is here more pronounced than in the preceding. In 
fig. 16 their extent is shown, when seen from above. "There are the elliptic lacun& of 
the three youngest or uppermost septa and it is seen how they expand towards the con- 
cave side of the shell and form only a narrow stripe along the convex side. Al the 
septa which succeed the third septum have been loosing in width, so that the sixth or 
