200 BRITISH PALZKOZOIC FOSSILS. [ Bracuropopa, 
varies considerably in depth, being sometimes rather less than the above dimensions, and having in one spe- 
cimen the proportion of 4; compared with the length, the width is sometimes a little more, and sometimes 
a little less than the measurement given above. Some specimens seem to shew projecting irregular transverse 
squamee of growth. 
Position and Locality—Occurs in great numbers in the greenish sandstone of Mulock quarry, Dal- 
quorhan, near Girvan, Ayrshire; Craig Head, near Girvan, Ayrshire. 
Explanation of Figures—P1. 1. H. fig. 6. Natural size, from the sandstone of Dalquorhan, shewing the 
entering valve and the foramen beneath the beak; 6a, Ditto, profile; 7, internal cast of receiving valve; 
8, internal cast of entering valve. 
HEMITHYRIS CRISPATA (Sow. Sp.) 
Ref. and Syn. = Terebratula id. Sil. Syst. t. 12. f. 11. 
Sp. Ch.—Longitudinally ovate, or subtrigonal, depressed; apical angle 100°; beak of receiving valve 
moderate, without distinct concavities at the sides; entering valve slightly convex, with an obscurely defined, 
rounded elevation, in the marginal third of the length; receiving valve very slightly convex near beak, and 
on the sides, with wide, shallow, rounded mesial concavity, extending from the margin to within one-third 
of the beak; lateral margins with a broad, slightly-curved wave towards the entering valve; middle of front 
margin elevated into a rounded sinus, twice as wide as high; six mesial, and six lateral plates on each side, 
all nearly equal, obtusely angular, and continued separately to the beak ; a considerable space at the sides 
smooth; shell fibrous; a moderate foramen beneath the beak. Length eleven lines, width the same, pro- 
portional length of entering valve {;, greatest depth of both valves ,%j. 
This species seems to me constantly distinguished from the H. Jacwnosa, with which several writers 
unite it, by the greater length and depression of the valves, small rounded front sinus, and larger smooth 
space on each side, as well as continuity of the lateral mesial ribs to the beak. 
Position and Locality—Aymestry limestone, Leintwardine, Shropshire. Apparently a wide variety of 
this species, (width one inch,) and proportionate length only =, but agreeing in number and character 
of ribs, general depression, &e. with the above, occurs in the limestone, Old Radnor to Presteign, Rad- 
norshire. 
Hemituyris Davipsoni (A/°Coy). 
Ref. and Syn.—id. M°Coy, Annals Nat. Hist. 2nd Series, Vol. VIII. p. 392.= Terebratula spherica Sow. 
Dayidson, Bull. de la Soc. Géol. de France, 2nd Series, Vol. V. t. 3. f. 36. (mot of Sow. Sil. Syst. 
nor Sow. Geol. Trans.) 
Sp. Oh—Globose, or subeuboidal; entering valve deeper than the receiving one, moderately convex 
on the rostral half, abruptly and obtusely bent over towards the margin, nearly at right angles; beak 
of the receiving valve small, with a minute triangular opening beneath the apex, moderately convex, de- 
pressed towards the margin, to form a broad, slightly-defined sinus, the corresponding ridge to which in 
the entering valve is scarcely elevated; lateral margins nearly straight, front margin elevated into a quadrate 
sinus twice as wide as high; valves radiated with from eighteen to twenty very obtusely angular, simple 
ridges, reaching distinctly to the beak, and deeply notching the margin, the four middle ones perceptibly 
larger than the rest. Length and width equal, and about five lines; proportional depth of deflected 
front =, depth of both valves =. 
This species differs from the Terebratula sphwrica (Sow.) Sil. Syst., by having the elevation of the 
front towards the entering valve, as in ordinary cases, instead of towards the receiving one as in that 
species, which, in consequence of this, Mr Davidson suggests to be a variety of H. deflexa. The 
Devonian Atrypa sphwrica (Sow.), to which the present fossil is referred by Mr Davidson, differs com- 
pletely by having all the rostral portion smooth, while the ridges extend clearly to the beak in this 
