TROCHOCERATID^. 
21 
Trochoceras distortum, Barrande. 
1865. Trochoceras distortam, Barrande, Defense des Colonies, iii. p. 33. 
1867. Trochoceras distortum, Barrande, Syst. Sil. de la Bohenie, vol. ii. 
pt. i. p. 98, pi. xxyiii. ff. 1 1-14. 
Sp. Char. Shell ver}^ clearly asymmetrical, when a sufficiently 
large portion is seen. The enrolment is sinistral. There appear to 
be only two whorls, which are in great part disconnected. The 
transverse section is elliptical ; the ventro-dorsal is to the transverse 
axis as 7 : 8, there being a tendency to a subquadrate form. The 
rate of increase is about 1 in 14, measured upon a fragment figured 
by Barrande (pi. xxviii.). The length of the body-chamber is ap- 
parently about twice the diameter of its base. The septa are 
numerous, their distance from each other equalling about of the 
ventro-dorsal diameter. The siphuncle is close to the convex border; 
its elements are slightly inflated between the septa. The test, 
preserved in the specimen from Xehou, marked only with fine lines 
of growth which conform to the contour of the whorls. 
Remarl's. The nearest ally of this species is Trochoceras David- 
soni, Barrande (pi. xxvii.), but the latter has a more rapid rate of 
increase, wider septa, and a more quadrate section. 
Hoiizon. Etage G ( = Downtonian). Devonian. 
Localities. Tetin, Lochkow, Bohemia; jS'ehou (Manche), France; 
(Devonian). 
Fairly weU represented in the Collection. 
Trochoceras Davidsoni, Barrande. 
1848. Trochoceras Davidsoni, Barrande, in Ilaidinger’s Berichte fiber 
die Mittheil. von Freund, der Naturwiss. in Wien, Band iv. p. 208. 
1867. Trochoceras Davidsoni, Barrande, Syst. Sil. de la Boheme, vol. ii. 
pt. i. p. 89, pi. xxvii. ff. 1-7. 
Sp. Char. Shell with only about two whorls, which are dis- 
tinctly asymmetrical, and not contiguous in any examples met 
with. The enrolment of the whorls is sinistral. The transverse 
section of the body-chamber is subquadrangular, but it is nearly 
circular in the septate part ; the ratio of the ventro-dorsal to the 
transverse diameter is as 5 : 6. The shell increases its diameter 
about three times in the course of the last volution. The body- 
chamber occupies nearly half of the last whorl. The septa are 
distant about ^ the ventro-dorsal diameter of the shell, measured at 
the upper part of the septate portion. The siphuncle is very near 
the convex border, sometimes not quite in the median line of the 
ventro-dorsal diameter ; its elements are slightly inflated in the 
