ORTHID A. 229 
beak, and gradually widening as it nears the front; hinge-area very narrow. Surface of 
both valves ornamented with numerous fine, angular, thread-like, bifurcating striz. 
Length about 7, width 8 or 9, depth 2 lines. 
Obs. Orthis Menapi@ is a small well-marked species, but is rarely found possessing its 
normal form, or its shell, nearly every specimen being more or less distorted from the effects 
of cleavage and fossilization, as is well exhibited in fig. 9. No very complete examples, or 
rather internal casts, having as yet been obtained, I have not attempted to describe 
its interior, but in figs. 11 and 12 will be seen the little we are at present acquainted 
with. 
Position and Locality. 'This species was discovered for the first time by Mr. Hicks at 
the base of the Arenig group, or Lowest Llandeilo, at Tremanhire, and subsequently at 
Llanveran, Ramsey Island, and Whitesand Bay, all near St. David’s; and the designation 
Menapie was assigned to it by Mr. Hicks, from the classical name of the earliest city men- 
tioned in the St. David’s district. It occurs in company with Orthis Carausii (Salter), 
but is easily distinguished from it by its shape as well as by the number and strength of 
its strie. I am not acquainted with the species from any other British or foreign 
locality. 
Ortuis Carausit, Salter, MS. PI. XXXIII, figs. 1—7. 
Ortuis Carausii, Dav. Geol. Mag., vol. v, p. 315, pl. xvi, fig. 23, July, 1868. 
Spec. Char. Suborbicular, rather wider than long; hinge-line as long as or a little 
less than the width of the shell; slightly indented in front. Dorsal valve very gently 
convex, with a longitudinal depression along the middle. Ventral valve deeper than the 
opposite one; beak small, incurved; area rather narrow. Surface of valves covered with 
about sixteen simple rounded ribs, and concave interspaces of about equal breadth. In 
the interior of the ventral valve the muscular area is small, and laterally margined by a 
prolongation of the dental plates. In the interior of the dorsal valve the cardinal process 
is very small, while a projecting ridge extends from its base to about half the length of 
the valve; muscular impressions very slightly marked ; brachial processes small. 
Length 7, width 8, depth 3 lines. 
Obs. This important species was discovered in the Lower Arenig or Lower 
Llandeilo rocks of St. David’s by Mr. Hicks about the year 1864. The shell occurs in vast 
abundance in the condition of internal casts and external impressions, mostly with their 
natural shape, in yellow sandstone at Tremanhire; and in an extraordinary state of dis- 
tortion in darker shales at Llanveran, Whitesand Bay, and Ramsey Island, St. David’s, 
Pembrokeshire. Indeed, so great is the state of distortion from the effects of cleavage that one 
example found by Mr. Homfray at Llanveran measured five lines in length by twenty- 
