0ETH0CEEATID3:. 
13 
nothing to separate Barrande’s from Miinster’s species, and I have 
therefore united them under the fii’st name applied to this form. 
The specimen in the Collection is badly preserved, and partly 
buried in the matrix, hut it retains a portion of the test, showing 
the very characteristic wavy riblets of this species. 
It occurs in Bohemia in Etages D, E, and E, that is, both in the 
Second and Third Eaunas. If I have rightly interpreted the Ordo- 
vician example in the National Collection, this species occurs in beds 
in Britain (Middle Bala) which have been correlated by Mr. Marr 
with bande cl 5 of Barrande. 
Horizon. Middle Bala. 
Locality. Ardwell, Ayrshire. 
Eepresented by one example. 
Orthoceras gracile, Portloek. 
1843. Orthoceras gracile, Portloek, Rep. on the Geol. of Londonderry, 
p. 366, pi. XXV. f. 2. 
1843. Orthoceras tuhicinella, Portloek, Rep. on the Geol. of Londonderry, 
p. 367, pi. XXV. ff. 3, 4. {Not of Sowerby.) 
1843. Orthoceras calamiteum, Portloek, Rep. on the Geol. of London- 
derry, p. 365, pi. XXV. ff. 1, a, b. (Not of Miinster.) 
1851. Orthoceras calamiteum, Salter, in Murchison’s “ Silurian Rocks 
of Scotland,” Quart. .Journ. Geol. Soc. vol. vii. p. 173. 
1851. Orthoceras annellatum, M‘Coy, in Sedgwick’s “ Geological Struc- 
ture and Relations of the Erontier Chain of Scotland,” British 
Assoc. Rep. p. 103. (Not O, anellum of Hall.) 
1852. Orthoceras bilineatum, M^Coy, British Pal. Eoss. fasc. ii. p. 319. 
1854. Orthoceras bilineatum, Salter, in Murchison’s ‘ Siluria,’ ed. i. 
p. 197, Eoss. Gr. 26. f. 2. 
1882. Orthoceras yracile, Blake, British Eoss. Ceph, pt. i. p. 85, pi. iii. 
tf. 5, 5 a, 9 a-c. 
Sj). Char. Section circular ; rate of increase about 1 in 9, de- 
creasing with age to almost zero. The ornaments consist of transverse 
undulations of very variable character, being sometimes wider than 
the interspaces, as in Portlock’s type, sometimes narrower, but 
tending to become less acute and conspicuous with age ; they occupy 
^ to 4 of the diameter. The minor ornaments consist of a cancella- 
tion over the surface. The septa are parallel to the ribs, and occupy 
the re-entering angle between them, and are therefore distant ^ the 
diameter. {Blake.) Siphnncle unknown. 
Remarks. The great variability of this species, as remarked by 
Professor Blake, must be regarded as one of its characters. 
Horizon. Middle Bala. 
Locality. Ardwell, Ayrshire. 
Represented by one fairly good specimen. 
