508 BRITISH PALAXOZOIC FOSSILS. [ LAMELLIBRANCHIATA. 
SANGUINOLITES VARIABILIS (M*Coy). PI. 3. F. figs. 6, 7, 8. 
Ref—M Coy, Ann, Nat. Hist. 2nd Series, Vol. VIT. 
Desc.—Oblong, tumid, nearly closed at the ends; averaging twice as long as wide (sometimes a little 
more, sometimes a little less); beaks large, tumid, oblique, close to the anterior end, which varies from one- 
ninth in large to one-seventh of the length in smaller specimens; anterior lunette large, smooth, oval, con- 
tracting the rounded anterior end; ventral margin nearly straight, or commonly with a wide, shallow, mesial 
sinus, very rarely with a slight convexity; valves evenly tumid, or with a slight broad mesial concavity or 
flattening ; posterior slope flattened, smooth ; defined by a diagonal, slightly sigmoid ridge, sharp and angulated 
near the beak, gradually becoming rounded and obscure towards the inferior posterior angle in old specimens ; 
greatest depths of the valves along this line, and at about half way from the beak; hinge-line with a slight 
upward curvature; posterior lunette very wide, concave, nearly horizontal; surface marked by concentric 
wrinkles yariable in size and strength, usually thickening slightly on reaching the diagonal posterior ridge, 
almost always undulated and irregularly interrupted about the middle and anterior third of the sides, (averaging 
five or six in the space of three lines from the beak, about the middle of the shell) ; periostraca sharply 
marked with close interrupted strie and a few minute scattered points, very rarely falling into close regular 
radiating lines; usual length about two inches, proportional width from beak to ventral margin =;, width of 
posterior end ;4, length of anterior end =>, depth of both valves ;;,- 
The irregular interruption and undulation of the concentric wrinkles in front of the middle of the sides is 
often very striking and beautiful, and is always recognisable. It is very variable in the thickness and regularity 
of the ridges; it most nearly approaches the S. regularis (King sp.=S. sulcatus Flem. sp.), from which it 
differs in the undulatory interruption of the ridge at the place mentioned, and in being rather shorter and 
more arched, and the greatest gibbosity of the shell being along the anterior boundary of the posterior slope, 
it being much nearer the anterior end, and the posterior portion being compressed in that species, in which 
also the greatest gibbosity is nearer to the dorsal margins, giving a much less tumid character to the lower 
part of the valves; it is possible, however, that they are varieties. From the Hdmondia sulcata it differs in 
the wrinkles not uniting into few large wrinkles in passing to the posterior slope, in their disappearing on the 
posterior slope, and in the generic characters. 
Position and Locality—Rare in the lower carboniferous limestone of the Isle of Man; not uncommon at 
Lowick, Northumberland ; rare in the carboniferous limestone of Berwick-on-T weed. 
Explanation of Figures.—P1. 3. F. fig. 6, right valve natural size, from the limestone of Lowick, North- 
umberland; fig. 6a, seen from behind, to shew the inflected dorsal margins; fig. 7, ovate variety, without 
byssal sinus, and with very fine concentric plice ; fig. 7a, small portion of surface of another specimen, highly 
magnified,‘shewing the lines of rough puncta crossing the concentric wrinkles and membranous strie of the 
periostraca; fig. 8, oblong variety. 
Genus. LEPTODOMUS (M°Coy). See page 277. 
LEPTODOMUS COSTELLATUS (M/°Coy). PI. 3. F. fig. 5. 
Ref—M Coy, Ann. Nat. Hist. 2nd Series, Vol. VII. 
Desc.—Ovato-oblong, very tumid; depth of both valves about equal to the width; anterior and posterior 
lunettes large, defined, shallow ; beaks very large, tumid, obliquely incurved, terminal; anterior side obtuse, 
subtruneate, slightly oblique beneath them; a small sinus in the ventral margin close to the anterior end, 
from which a narrow, slightly marked concavity extends nearly to the beaks, close to the anterior edge; 
hinge-line nearly as long as the shell, with a slight upward curvature ; posterior end contracted, arched up- 
wards, slightly oblique, subtruncate ; ventral margin strongly convex behind the sinus ; posterior slope abruptly 
compressed, smooth, or with a few lines of growth parallel with the margin, divided nearly in the middle by 
a small sulcus from behind the beaks; sides marked with numerous small, regular, close, narrow, subangular 
