Bracutopopa.| DEVONIAN MOLLUSCA. 387 
arched ; surface radiated with very delicate, straight, rough, simple, sharply defined ridges, almost uniform in 
size and closeness throughout, separated by flat coarsely punctured spaces, equalling them in width; strize 
increasing in number by intercalation only, giving rise to a slight appearance of alternation of size in some 
spots; about eleven strize in two lines about the middle, and nearly all parts of the shell when unpressed, but 
varying from eight to sixteen by distortion in the rock; casts of entering valve shewing the impression of a 
strong mesial septum, reaching rather more than half-way to front margin, and two short, thick, cardinal teeth ; 
receiving valve with two, moderate, straight, dental lamellze, diverging at 125°. Average width about one inch, 
proportional length varying (most probably from pressure) from ;% to ;, (sometimes 13 inch wide). 
The coarse punctation of the sulci gives a rugged character to the strize; besides, I have noted also 
in parts a slight tuberculation of the strize, although I see no marked change of character in them towards 
the margin, as suggested by Phillips. I suspect the Linton shell referred by Prof. Phillips (Pal. Foss.) to the 
Silurian O. compressa, belongs to the present species. 
Position and Locality.—V ery abundant in the hard Devonian schists of Linton. 
LepTm@NA (Strophomena) UMBRACULUM (Schlot. Sp.) 
Ref. and Syn. = Terebratulites umbraculum Schlot. Pet. p. 256. 
Sp. Ch.—Truncato-orbicular ; hinge-line nearly or quite equal to the width of the shell; ears rectangular, 
or slightly obtuse; cardinal area wide, inclined backwards at an angle of about 140°; foramen slightly wider 
than a right angle, closed by a concave cicatrix; front and lateral margins nearly uniformly arched or slightly 
subquadrate ; receiving valve convex near the beak, which is slightly prominent, becoming gradually concave, 
after four or five lines, towards the margins; entering valve convex, with a slight mesial depression; greatest 
depth about the middle; surface of both valves radiated by straight thread-like ridges, separated by slightly 
wider coneave spaces, which are either smooth, or crossed by fine transverse lines of growth (not minute, 
irregular wrinkles, as in S. crenistria), usually each alternate line smaller (to allow for the increase of number 
towards the margin), very rarely near the margin of large specimens three smaller between some of the 
pairs of larger; six to eight striee in the space of two lines at one inch from the beak ; six in the same space 
at an inch and half from the beak. Width (of very large specimen) two inches four lines, proportional 
length %, depth about =, width of area two lines, width of small specimen ten lines, proportional length of 
receiving valve =, depth =. 
This species is distinguished from the O. crenistria by the greater convexity of the entering valve with 
its slight mesial depression, also by the thicker, closer, and more equal strize, the narrow spaces between which 
are either quite smooth, or only marked by regular transverse lines of growth, totally different from the deep, 
minute, irregular wrinkles of the carboniferous species. I suppose the Orthis crenistria of Phillips’s Palzeozoic 
Fossils may possibly be this species, as well as the Spirifera crenistria mentioned by Sowerby from Plymouth ; 
but in neither case is the figure or description careful enough to allow of any definite opinion being formed. 
Position and Locality—Common in the limestone of Teignmouth. 
Subgenus. STROPHALOSIA (king). 1844. 
= Leptenalosia King. = Aulosteges Helmerson (1847) = Orthothria Geinitz (1848). 
Gen. Char.—Subhemispherical, both valves bearing scattered tubular spines; receiving valve conyex ; 
entering valve concave externally; hinge-line straight, nearly as long as the shell is wide; cardinal area 
distinct in one or both valves, the rostral tooth forming a boss in the middle of that of the entering valve, and 
the triangular foramen in the middle of the opposite area nearly closed by a pseudo-deltidium. Interior of 
receiving valve with large, longitudinally ovate, muscular impressions in the cavity of the beak, and a strong 
pair of conical hinge-teeth, one on each side of the base of the aperture: interior of entering valve with a thick, 
prominent, rostral tooth, from which a mesial septum extends about half way to the margin; on each side of 
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