406 BRITISH PAL-KOZOIC FOSSILS. [CepHaLopopa. 
broad sides; a specimen one inch nine lines in diameter at the large end, and three inches long, tapers to one 
inch four and half lines ; septa direct, concave, three lines apart at an inch in diameter; four lines apart at two 
inches in diameter; two and half lines apart at seven lines in diameter; surface covered with rough, very fine, 
elevated, thread-like striz, slightly varying in thickness irregularly ; usually subequal and their own thickness 
apart ; occasionally more distant, with one finer line between the larger; about fourteen longitudinal striz in 
the space of one line at an inch in diameter. 
I have little doubt that the S. Petherwin and Marwood shell, referred by Prof. Phillips to the Silurian 
O. Ludense, belongs to this species, on which I have observed the striation on several parts of specimens collected 
by myself from the former locality. 
Position and Locality.—Very abundant in the limestone associated with the slate of S. Petherwin, 
Cornwall. 
Subgenus. CYCLOCERAS. See page 318. 
CYCLOCERAS STRIATULUM? (Sow. Sp.) 
Ref. and Syn. = Orthoceras striatulum Sow. Geol. Trans. 2nd Series, Vol. V. t. 54. f. 20.+0. ibea Sow. 
Phill. Pal. Foss. f. 208 (not of Sow.) = O. calamiteus Miinst. 
Sp. Ch.—Rapidly but irregularly tapering when old at about an angle of 17°, more gradually tapering when 
young at an angle of about 12°, slightly compressed ; surface with very prominent obtusely-angular rings, rather 
more than their thickness apart, slightly waved on the sides, crossed by strong, longitudinal, thread-like striz, 
nearly twice their thickness apart, with a very fine intermediate line between each pair; five of the larger strive 
in two lines at a diameter of one inch nine lines; six in the same space at a diameter of six lines; three rings 
and two interannular spaces in a space of one inch, at one inch 6 lines in diameter ; three rings and two inter- 
annular spaces in six lines at six lines in diameter ; section broad, oval, its width = of the lengths siphon slightly 
eccentric towards one of the broad sides. 
The longitudinal striation, if only the large striz be counted, is in this species of the same size and 
relative distance as in the O. tubicinella, so that this point of distinction given by Sowerby and Prof. Phillips 
does not hold good ; but when specimens of the same size are compared O. tubicinella has closer rings. It is to 
this species that, I think, the O. calamiteus of Mister belongs. 
Position and Locality —Common in the limestone and shale of S. Petherwin. 
CYCLOCERAS TUBICINELLA (Sow. Sp.) 
Ref.=Orthoceras tubicinella Sow. Geol. Trans. 2nd Series, Vol. V. t. 57. f. 29. 
Sp. Ch.—Shell tapering at an angle of about 10°, crossed by very prominent, rounded, slightly oblique 
rings, their own thickness apart, crossed by strong, longitudinal, thread-like striz, nearly twice their thickness 
apart, five in two lines on nearly all parts of the shell; three annular ridges‘and two interannular spaces at 
seven lines in diameter, four ridges and three interannular spaces in three lines, at three lines in diameter ; 
section nearly circular, very slightly compressed ; siphon central. A specimen four and half lines in diameter 
at the large end, and two inches long, is three lines in diameter at the small end. 
From the roughness of the stone I cannot be quite sure whether there are any intermediate longitudinal 
strize between the strong ones which I mention. It is not probable that the subsequently described O. calamente 
(Miinster) is identical with this species, as he figures his species with much more distant rings, and it is there- 
fore, I think, more probably referrible to the O. striatulum. : 
Position and Locality—Common in the Devonian limestone of Plymouth. A 
