46 
NAUTILOIDEA. 
where the preceding one comes in contact with it. The body- 
chamber in the type specimen occupies ^ of a whorl. The section 
is distinctly quadrangular, the convex side being broader than the 
concave. The septa are rather numerous, their distance upon the 
sides of the shell being about 3 lines where the diameter is about 
1 inch. The sutures form a broad and shallow sinus on the sides, 
and bend sharply forwards upon the lateral angles, making a broad 
and shallow sinus again on the convex side. The siphuncle is 
situated close to the concave border of the shell. The first whorl 
is ornamented with fine and regular transverse raised lines, 5 or 6 
in the space of 1 line. At a later stage these give place to irregular 
lines of growth, which at intervals of 1 to lines assume the 
character of riblets, becoming stronger upon the periphery, where 
in adult shells they almost pass into ribs. The whole of the test, 
which is very thick, and composed of several layers, is covered with 
fine transverse lines of growth. Owing to weathering, and in some 
cases to changes brought about by fossilization, the surface of the 
test sometimes assumes a very different character from that which 
it presents when well preserved. Some of the figures, for example 
(notably Eoemer, loc. cit. pi. vi. f. 2 6), represent the lines of growth 
as minutely waved ; but this appearance, judging by specimens I 
have examined, is due merely to the exfoliation of the edges of the 
laminae of the test. 
Remarhs. The type specimen of Trocholites undosus (preserved in 
the Museum of the Geological Society) is much crushed and distorted, 
so that many of the septa (except those near the body-chamber) are 
closer together than they would naturally be. Those near the body- 
chamber are 2 lines apart. The sutures are strongly bent forwards 
at the lateral angles. The whorls have the subquadrate section 
characteristic of the Norwegian specimens in the British Museum 
Collection, and as figured in the works cited above. There are 
some very obscure and irregular prominences on the type specimen, 
which appear to be due simply to unequal erosion of the surface of 
the cast, and are not of the nature of ribs as represented in Sowerby’s 
figure, in which they have been considerably intensified. 
Horizon. Etages 4 and 5 a (Bala Series). 
Localities. Porsgrund, Klosterfos Waterfall near Skien, Sandviken 
near Christiania, Hero (Hardanger Pjord) : Norway. 
Eepresented in the Collection by several very fine specimens, 
some of which were transferred from the Museum of Practical 
Geology. 
