TROCHOCERATID^. 
37 
Trochoceras asperum, Barrande. 
1848. Trochoceras asperum^ Barrande, in Haidinger's Beri elite liber die 
Mittheil. von Freund, der Natiirwiss. in Wien, Band iv. p. 208. 
1867. Trochoceras asperum, Barrande, Svst. Sil. de la Bobeme, vol. ii. 
pt. i. p. 104, pi. xvi. ff. 8-16, pi. xix. ff. 18, 19. 
1882. Trochoceras asperum, Blake, British Foss. Ceph. pt. i. p. 218, 
pi. xxix. f. 3. 
Sp. Char. The shell in this species consists of two whorls in 
which the asymmetry is hut slight. The enrolment is sometimes 
dextral, sometimes sinistral. The transverse section is elliptical, 
the dorso-ventral diameter being in the ratio of 6 to 5 to the trans- 
verse. The shell increases its diameter about twice in the course of 
the last volution. The body-chamber leaves the coiled portion and 
is continued in a straight line, the length of the freed portion, how- 
ever, varying in different individuals. The ornamentation consists 
of acute, oblique annulations, whose average distance from summit 
to summit is about 2 lines ; they form a deep sinus on the convex 
side of the shell, and are but feebly marked on the concave side. 
The test is covered with longitudinal lines which are very variable, 
and are crossed by much finer transverse lines. The septa are 
numerous, their average distance apart, as measured at the sides of 
the shell, being about lines. Their surface is strongly convex, 
but they are only slightly curved. The siphuncle is midway between 
the centre and the convex border. 
liemarhs. Professor Blake has identified this species in the British 
Silurian. He observes that “ the chief difference between these 
[British examples] and the Bohemian type is the rarity of any longi- 
tudinal lines, but these are variable, and may easily be lose in the 
preservation of the fossil. Hevertheless a somewhat similar fossil 
from the Upper Ludlow shows longitudinal lines, but this may be a 
distinct species, e. g. Trochoceras Sanclheryeri. The septal characters 
also render the determination doubtful, yet the general proportions 
and ornaments, especially the nature of section, which is rare among 
Trochocerata, the prominence of the ribbing, and the changes in the 
body-chamber, which are the chief features in the Bohemian, are 
seen in the English examples.” 
The straightness of the body-chamber and the character of the, 
ribbing distinguish T. asperum from other Bohemian species. 
Horizon. iStage E ( = Salopian). 
Locality. Wiskocilka, Bohemia. 
Kepresented in the Collection by a single example.. 
