NAHTILID^. 
81 
Remarls. The difference between this species and i>. Bohemictim, 
its nearest ally, has already been pointed out. 
Horizon. Etage E (= Salopian). 
Locality. Lochkow, Bohemia. 
Fairly well represented in the Collection. 
Barrandeoceras tyrannus, Barrande, sp. 
18G7. Xautilus tyrannus, Barrande, Syst. Sil. de la Boheme, rol. ii. 
pt. i. p. 148, pi. xxxviii., pi. xxxix. ff. 9-11, pi. xl. 
1877. Xautilus tyrannus, Barrande, ibid., Snpplem. et Serie tardive, 
p. 200, pi. cccclxxvi. case i (young), pi. cccclxxxix. case ii (initial 
point, showing cicatrix), pi. dxliv. 
1883. Barrandeoceras tyrannus, Hyatt, ‘‘ Genera of Fossil Cepha- 
lopods,” Proc. Boston Soc. i^sat. Hist. vol. xxii. p. 299. 
Bp. Char. Shell discoid, flattened, forming from three to four 
whorls, the ratio of their breadth to their thickness being as 2 : 1 ; 
all are exposed, and there is a considerable vacuity in the centre. 
The whorls are only just touching, so that there is scarcely any 
impression upon the concave side. The umbilicus is wide but 
shallow. The initial portion of tlie shell has the form of a little 
hook, and makes scarcely half a volution. The transverse section 
is ovate, the larger extremity corresponding with the concave side 
of the shell, the opposite or peripheral side being narrowly rounded. 
The ventro-dorsal is to the transverse axis as 2 : 1. The whorls 
increase in diameter in the ratio of 2 : 7. The body-chamber 
occupies a little more than half the last whorl. The aperture is 
situated in the plane of the last septum. The septa attain a 
maximum distance from each other representing 4 of the ventro- 
dorsal diameter, and their convexity is equal to 5 of the same. 
The sutures form a wide shallow sinus upon the sides of the shell, 
and are strongly arched upon the periphery. The siphuncle is 
situated a little above the centre; its elements are cylindrical. 
The test is ornamented with oblique strim of growth, which in the 
young shell are tolerably regular, fine, and close-set. On the last 
whorl in the adult shell they become more unequal, both in strength 
and distance, from each other ; sometimes, again, they are separated 
by wide grooves ; they always form a deep sinus upon the peri- 
phery. There are traces of longitudinal stria) upon the young shell, 
as is commonly the case in many genera of the Hautilidoe. The 
cast of the body-chamber is covered with epidermids. 
RemarJes. This species attains a larger size than any of its con- 
geners in Bohemia. Barrande estimates the diameter of some 
specimens in his collection at 300 millim. The nearest species to 
PAKT II. G 
