152 
BTATITILOIDEA . 
horizon of the second fanna ” (Ordovician). The matrix of the 
specimen in the British Museum (which is one half of the 
individual collected by de Eottermund, the other half being in the 
museum of the Jardin des Plantes, Paris) is a buff-coloured lime- 
stone, resembling that of Thessalon Island (Lake Huron), which 
has been assigned to the Black Biver Pormation, and this is 
probably the horizon to which the present species belongs. If this 
be correct it corresponds very nearly with that of E. suhannulxitum, 
Whitf., from “ the upper part of the buff limestone of the Trenton 
group, near Beloit, Wisconsin.” 
Another fragment in the Collection, much weathered and battered, 
exhibits characters which ally it with E. Eottermundi, especially 
the close proximity of its septa, and its large, marginal siphuncle. 
This also is from Lake Huron, but the precise locality has not 
been recorded. There is little doubt that the specimen figured, 
but not described, by Bigsby (/oc. cii.) is conspecific with the present 
species. 
Horizon. Black River Formation ( = Llandeilo Limestone). 
Locality. Lake Huron (Canadian side). 
Represented by two specimens, one of which is the type figured 
by Barrande (loc. cit.). 
Endoceras gladius. Holm. 
1845, Orthoceratites duplex, 'Mm'ch.., de Vern., & de Keyserl. G<5ol. de la 
Russie d’Europe, p, 351, pi. xxiv. f. 7 (not pi. xxv. f. 2). 
1885. Endoeeras gladius, Holm, Palaeontologische Abhandl. Band hi. 
Heft i. p. 13, Taf. ii., Taf. hi. f. 1 a-i, Taf. v. f. 1. 
8p. Char. Shell straight. Section apparently circular. The rate 
of increase may be computed roughly at about 1 in 7. The septa 
are widely separated, being distant about 10 1 lines where the shell 
has a diameter of 2| inches. They are strongly concave, and run 
a considerable distance up the inner side of the shell. Their depth 
scarcely equals ^ of the shell-diameter. The siphuncle attained a 
diameter of probably nearl;^ half that of the shell, though owing 
to the imperfect condition of the type specimen it was impossible 
to obtain an accurate measurement. There is a strongly inflated 
rim in the casts of the siphuncle where the necks of the septa 
overlapped. The outer shell appears to have been smooth and 
without ornaments of any kind. 
Remarks. I have derived most of the characters of this species 
from Dr. Holm’s careful and detailed description of it. In the 
admirable figures he gives those upon plate ii. (f. 3 a-c) represent 
