RACHIOPODA. | UPPER PALAZOZOIC MOLLUSCA. 451 
greater part of the shell in most specimens (nine to eleven in two lines at eight lines from the beak), towards 
the margin every fifth becoming more prominent than the rest; on all parts the radiating strize have the inter- 
vening wider concave spaces crossed by subregular concentric ridges, usually the same distance as the strize 
apart, and sometimes nearly equalling them in strength, producing a slight nodulation of their sides ; intervening 
spaces under the lens coarsely punctured. Width of average-sized specimens one inch seven lines, proportional 
width of hinge-line =, length of approximately horizontal portion of entering valve %, of deflected front *, 
depth of entering valve 3, space between the valves about +, height of cardinal area about \,. 
This species seems to have the striation closer and more uniform than the 8. crenistria, from which it is 
totally distinguished by the nearly hemispherical form and semi-cylindrical produced front of the adult entering 
valve, as well as the different inclination of the cardinal area and strong sigmoidal flexure of the receiving valve. 
When small specimens under an inch long are compared (before the front is developed), the entering valve is 
completely distinguished from the corresponding part of the S. crenistria by its great gibbosity, and by its short 
hinge-line, regularly arched into the rounded sides, corresponding specimens of the S. crenistria being flat, and 
with acute ears extending beyond the sides. 
Position and Locality—Common in the dark lower limestone of Lowick, Northumberland. The original 
Irish locality (in which the species is very common) is the red limestone, resembling that of Closeburn, at Castle 
Espie, co. Down, near the base of the Irish carboniferous system. 
Leprm@na (Strophomena) Ketiyt (M°Coy). 
Ref. and Syn. = Orthis Kellyi M°Coy, Synop. Carb. Foss. Irel. t. 22. f. 4. 
Dese.—Truneato-orbicular, or nearly quadrate; from the very slight convexity of the sides, and from the 
nearly straight or slightly sinuate wide front; nearly equivalved ; hinge-line as wide as the shell or nearly so, 
forming slightly obtuse or nearly rectangular cardinal angles; entire margins nearly in one horizontal plane. 
Entering valve slightly convex, becoming gradually flattened towards the cardinal line, divided in the middle by 
a wide, rounded, mesial hollow, which extends from the beak to the front margin, which it slightly sinuates. 
Receiving valve slightly convex near the beak, becoming gradually flattened or very slightly concave towards the 
side margins, middle elevated into a wide, obscurely defined, obtusely angular ridge, extending from the beak to 
the front margin; cardinal area moderate, inclining backwards at about 130°; both valves radiated with fine 
filiform ridges, alternately larger and smaller near the beak, more usually three smaller (the middle one largest) 
between each of the principal pairs near the margin; flat intervening spaces very minutely striated longitudinally 
under the lens, and coarsely punctured (sometimes seven or eight of the microscopic longitudinal striae) between 
each pair of ridges at the margin; in other states of preservation the strize seem closer and of more nearly equal 
thickness over the whole surface ; transverse wrinkles usually much closer and finer than in the S. erenistria ; 
specimens after one inch and quarter long shew the thick imbricating interruptions of growth marking the adult 
shell. Width one inch eight lines, proportional length of receiving valve 7%, of entering valve 4, depth of 
entering valve ;;,, of receiving valve ;;,, space between the valves ,, height of cardinal area 3°. 
This species occurs in vast profusion in that part of the carboniferous series called the arenaceous limestone 
by Dr Richard Griffith, developed under part of his carboniferous slates, nearly at the base of the earboniferous 
series of Ireland. It seems to be constantly distinguished from the S. crenistria by its rounded mesial furrow, 
which indents the front margin, also its more quadrate outline, shorter hinge-line, and small size, the largest 
specimens scarcely exceeding an inch and half long; and these and even smaller are shewn to have attained their 
usual adult size by the imbricating thickened interruptions of growth near the margin. The S. crenistria grows 
frequently to double this size without shewing the same signs of age; the sides of the entering yalve are also 
more convex, and the cardinal angles obtuse. The striation is so variable in these shells, according to the state 
of preservation of the surface, that it is of little use in specific distinctions; the strize, however, of the 
S. Kellyi, although resembling in character those of S. crenistria, are usually somewhat finer, closer, and more 
equal than in that species. 
