CrepHatopopa. | LOWER PALZOZOIC MOLLUSCA. 317 
ORTHOCERAS SUB-UNDULATUM (Porth.) 
Ref. and Syn.—Port. id. id. Geol. Rep. t. 28. f. 2 = Creseis Sedgwickit Forbes, Proc. Geol. Soe. p. 146. 
f, 2 (mala). 
Sp. Ch.—Shell tapering at the rate of one line in one inch from a diameter of six lines, at which size the 
shell is girt with oblique, gently and very slightly, waving sharp strize, three in one line, separated by flat spaces 
(shewing traces of parallel intervening strice under a strong lens) four or five times the width of the strize ; at 
two inches from the apex the diameter is two and half lines, and there are scarcely four oblique strize in one line. 
‘The septa in this species are indistinct and seem to coincide with the strize in direction. The strize sometimes 
appear elevated, sometimes impressed ; but I should think this is owing to the mode of preservation. Some 
large specimens, varying from one and quarter to two and half inches in diameter, seem to belong to the same 
species, having a striation very much of the same aspect, though disposed in irregular slightly oblique waves, 
varying in each specimen from six to eight in the space of two lines; in these the section is clearly a broad 
oval with the siphon of moderate size and less than its own diameter from the centre. 
Position and Locality.—Of the large examples, Upper Ludlow quartzite of High Thorns, Underbarrow, 
Kendal, Westmoreland; Upper Bala (Coniston flag) of Helms Knot, Dent; greenish Upper Ludlow schists of 
Mortimer’s Cross, Aymestry, Herefordshire ; and green flags (Wenlock shale) of Clungunford, Shropshire. 
The smaller and more usual types are from Upper Bala flags of Coldwell, Westmoreland, and olive schists 
above the Coldwell flags, near the Castle; in calcareous schists, hill-top, on road from Coniston to Hawkshead, 
Lancashire ; Lower Ludlow flags of Craig ddu alt, Llangollen, Denbighshire ; olive (Wenlock shale) flags of 
Howgill Fell, near Sedbergh, Kendal, Westmoreland ; olive mudstone (Wenlock shale) of Llangynyw Rectory, 
near Welchpool, Montgomeryshire ; Upper Bala flags of Ash Gill, Westmoreland; black Upper Bala shale 
of Builth Bridge, Radnorshire; olive Lower Ludlow schists of Leintwardine, Shropshire ; flags of Moel 
Seisiog, Llanrwst, Denbighshire ; mudstone of Lower Ludlow rock, Garden Quarry, Aymestry, Herefordshire ; 
Wenlock shale of Wenlock, Shropshire ; schists of Wellfield, Builth ; black Upper Bala (Coniston flags) of 
Dry Ridge, near Horton, Yorkshire. 
ORTHOCERAS TENUICINCTUM (Portk.) 
Ref.—Port. id. Geol. Rep. p. 371. t. 27. f. 5. (strize three or four times too far apart). 
Sp. Ch.—Shell very elongate, conic, tapering at the rate of half a line in one inch, from a diameter of ten 
lines, at which size the septa are five and half lines apart, two and half lines apart at a diameter of five lines, 
and slightly oblique, parallel with the strize, which are extremely fine (about sixteen in two lines,—or fourteen at 
a diameter of four lines), subequal, and scarcely their own thickness apart, and with a very gentle sigmoid wave 
on the sides, and wide dorsal and ventral curves. 
This species differs from the O. bacillus (Eichw.) and 0. linearis (Miinst.) by tapering much more slowly 
and having much fewer striz in a given space. I have not seen the siphon distinctly, but it seems to be nearly 
central. 
Position and Locality——In the dark limestone of the hill-top on road between Coniston and Hawkshead, 
Lancashire ; common in the Upper Bala flags of Coldwell, Westmoreland; in the Upper Ludlow rock of 
Kendal, Westmoreland ; schists of Dinas Bran, Llangollen, Denbighshire; Upper Ludlow rock of Woolhope. 
ORTHOCERAS TENUISTRIATUM (J/iinst.) 
Ref—Miinster, id. Beitr. 3. t. 19. f. 4. 
Sp. Ch.—Tapering at the rate of one line in one inch, from a diameter of five lines, at which size the septa 
are slightly more than one line apart; surface with close, equal, longitudinal striee, about twelve in one line; 
section broad-oval. 
