28 
NATJTILOIDEA.. 
Trochoceras arietinum ?, Barrande. 
1867. Trochoceras arietinum, Barrande, Syst. Sil. de la Boheme, vol. ii. 
pt. i. p, 103, pi. xvii. ff. 1-4, pi. xxv. ff. 1-3, pi. ciii. ff. 8-11. 
1882, Lituites? arietinus, Blake, British Foss. Ceph. pt. i. p. 227, 
pi. xxxi, ff. 4, 4 a. 
Sp. Char. The specimen figured by Barrande (pi. xxv.), although 
exhibiting very little of the body-chamber, shows that the shell was 
composed of at least two entire whorls. The asymmetry, though 
not very well marked, is sufficiently apparent. The enrolment is 
dextral. The transverse section is an oval of which the ventro- 
dorsal is to the transverse axis as 4:5; it is flattened upon the 
convex border. The body-chamber appears to have been of con- 
siderable length, probably occupying about | the external whorl. 
The septa are moderately distant from each other, being about 
I the ventro-dorsal diameter apart near the body-chamber. The 
siphuncle is at a little distance from the centre, towards the convex 
border. The ornaments consist of acute and separate transverse 
annulations which curve obliquely backwards, becoming obsolete 
along the convex border, where there are only lines of growth. 
These follow the same direction as the annulations, being faint 
upon the sides, but becoming stronger on the convex border. 
There are obscure traces also of longitudinal lines on the concave 
side. 
Remarhs. Professor Blake remarks {loc. cit. p. 228) that “ the 
only differences between our English specimens and the Bohemian 
are that the section is not transverse in the former ; but none of the 
specimens are uncompressed : also that no longitudinal lines have 
been observed, and the septa are a little wider apart. The re- 
markable proportions, the flatness of the front, and the character 
of the ribs, including their dying off on the front [border], are well 
exemplified.” 
One of the specimens which I have doubtfully referred to the 
present species is embedded in a slaty rock, and is consequently 
very badly preserved ; the pressure, however, coming from above, 
rather than laterally, has not distorted the outline of the fossil. 
About 2^ inches of the straight portion is seen, and this is less 
crushed than the coiled part. The other example is more satis- 
factory. In this the annulations agree in character with Barrande’s 
figures, and they appear to vbecome obsolete on the outer border of 
the shell, a crucial character of this species. The septa are seen to 
be wide apart, another feature in common with T. arietinum. 
