Bracuropvopa. | UPPER PALAOZOIC MOLLUSCA. 447 
Genus. ORTHIS. See page 212. 
ORTHIS CONNIVENS (Phill. Sp.) 
Ref. and Syn. = Spirifer id. Phill. Geol. York. Vol. IL. t. 11. f. 3.= 0 striatula Schlot. de Koninck, Foss. Bel. 
t. 13. f. 12 (mot of Schlotheim). 
Dese.—Rotundato-oblong, very inequivalve. Entering valve deeper and longer than the receiving one, 
extremely gibbous in old specimens; lateral margins nearly straight, very faintly sigmoid ; middle of front 
margin with a very shallow wide elevation towards the entering valve; hinge-line much less than the width 
of the shell; sides broadly rounded, greatest width about the middle, middle of front slightly sinuate ; beak 
very large, obtuse, inflated, extending considerably beyond the hinge-line and a little beyond the beak of 
the receiving valve; profile very much arched; greatest depth at one-third from the beak; a faint, shallow, 
mesial depression to the slight sinus in the middle of the front; sides steeply arched towards the margins. 
Receiving valve with a small, slightly prominent beak; cardinal area triangular, nearly at right angles to the 
plane of the lateral margins; rostral portion very slightly convex for four or five lines round the beak; sides 
flattened, sloping rather abruptly towards the margins, after five or six lines from the beak, the middle is 
depressed into a wide, plano-concave, shallow sulcus, corresponding with the sinus in the front margin. Surface 
with numerous, rather strong, concentric imbrications of growth about a line apart; surface longitudinally 
marked with very irregularly unequal, subequal, longitudinal sulci, rather less than their thickness apart, of 
nearly equal size on all parts of the shell (averaging ten or eleven in two lines, at six lines from the beak), the 
elevated strize rounded, or very obtusely subangular, occasionally di- or tri-chotomising at irregular distances, 
often with the branches reuniting, those on the sides divaricatingly arched; here and there some of the strize 
become rather rapidly more prominent, as if to rise into spines, then are abruptly reduced to less than their former 
size; ridges and sulci under the lens minutely granulo-punctate. Width of large specimen one inch one line, 
proportional length of entering valve *,, length of receiving valve ;%, width of hinge-line y,, height of cardinal 
area ;4,, width of sinus in front margin about &, depth thereof about 74, depth of receiving valve 77, depth of 
entering valve 4; width of young specimen nine lines, proportional length of entering valve =, depth of both 
valves *. 
It is difficult to say positively whether this is or is not a distinct species from the O. resupinata ; the enter- 
ing valve distinctly exceeding the receiving one in length, its very great gibbosity, more distinct mesial hollow, 
and slightly coarser strize, with less distinct and less numerous spine-like truncated thickenings of the striz, as 
well as the slight notch in the front margin, from both valves having a slight mesial hollow,—all these characters 
seem so much more strongly marked in the O. connivens, than in the O. resupinata, that it is very probable they 
are distinct species, more especially as the former fossil becomes so rugose from the number and strength of the 
concentric imbrications of growth, that it is obvious it reaches its adult size at about one half the linear dimen- 
sions of the O. resupinata. ‘This species differs from the Devonian Terebratulites striatulus of Schlotheim, to 
which it has been referred by M. de Koninck, by the very much greater depth of both valves in moderately 
large specimens, the great gibbosity of the entering valve, as well as its less definite mesial hollow, and less 
regular striation. 
Position and Locality—Rare in the carboniferous limestone of Derbyshire, and in the lower carboniferous 
limestone of Lowick, Northumberland. 
OrtHIs GIBBERA (Porth. Sp.) 
Ref. and Syn. = Atrypa gibbera Portk. Geol. Rep. t. 88. f. 1. Orthis id. M°Coy, Syn. Carb. Foss. Irel. t. 18. f. 9. 
Dese.—(Young) truncato-orbicular, convex, front margin slightly raised: (adult) semicylindrical, depth 
exceeding the width; sides subparallel, rostral portion of the shell flattened or moderately convex; front of 
both valves, after about nine lines from the beak, deflected nearly at right angles, much produced, rounded at 
[fasc. 11. ] 3M 
