OF RHYMNEY AND PEN-Y-LAN, CARDIFF. 497 
the posterior angle of the shell, dividing the posterior two thirds of 
the shell into a swollen anterior and a compressed posterior and 
superior part, which ends above in the straight hinge, and behind in 
the rounded end of the shell. Shell ornamented with longitudinal 
rounded ribs, 00375" apart, commencing from the edge of the 
lunule, and continuing along the valves till they reach the post-um- 
bonal ridge, past which the shell is smooth up to the hinge-line. 
Length $3"; breadth 3," ; thickness ,%,". 
Remarks. This shell was found by Mr. John Storrie near Cross 
Dowton, Rhymney, not far from the outcrop of the Ludlow beds. 
It was imbedded in a stray fragment of rock lying by the road-side, 
and not in situ, but so exactly similar in lithological character to 
the adjacent Ludlow beds that no hesitation need be felt in referring 
the shell to their horizon. 
The hinge-line does not show any transverse plaits ; but a slight 
inflection of the valve indicates apparently a cartilage-plate. There 
is no sign of an escutcheon. 
4 Lena? ampicva, sp. nov. (PI. XXIV. fig. 7.) 
Shell oblong ovate, compressed ; hinge-line short and straight ; 
margin of valves simple, elliptical, closed ; umbones anterior, directed 
slightly backwards, their posterior edge continued into a ridge 
ending on the upper part of the posterior margin. Surface covered 
with exceedingly fine close concentric stric. 
Length $8”; breadth 5%," 
Toot. As the saheralan ‘of the shell is not visible, and we do not 
know the characters of the hinge, its reference to Leda is in the 
highest degree doubtful. I have preferred, however, to assign it to 
this genus with a query rather than to make a new genus to receive 
it. In general form it is more like a Voldia, while in the character 
of its striation it exactly resembles Leda intermedia, Eth., from the 
Carboniferous formation. It is in the form of its posterior region 
that it differs most markedly from both Voldia and Leda. 
5. AMBONYCHIA ? TUMIDA, sp. nov. (Pl. XXIV. fig. 9.) 
Shell obliquely trigonal, tumid, truncated in front; anterior 
aspect heart-shaped ; umbones quite anterior, somewhat spirally 
incurved; hinge-line short and straight; margins simple, close, 
rounded; a small posterior wing or compressed upper posterior 
region; surface very finely concentrically striated. 
‘Length 48"; breadth +2”; thickness near beaks, where it is 
thickest; 43", 
Remarks. It is by no means certain that this species is an Am- 
bonychia; the specimen on which it is founded is not quite perfect in 
front, and might have possessed a small anterior wing. It is some- 
what similar to Amphicelia, Hall. To give a rough idea of its 
general form, one may compare it to some species of Isocardia os 
gr. I. nitida, Phillips), or to some forms of Pholadomya. 
2u 2 
