212 BRITISH PALASOZOIC FOSSILS. [ Bracuropopa. 
Genus. PORAMBONITES (Pand.) 1830. 
Syn. = Isorhynchus King 1850 (not of Schénherr). 
Gen. Char.—Subglobose, depressed, entering valve largest; beaks obtuse, subequal, separated by a 
small cardinal area in each valve; foramen in each valve small, triangular, reaching the hinge-line ; two long 
slightly diverging dental lamellee in each valve, those of the receiving valve closest together; surface coarsely 
punctured in lines. 
I am unable to state the true generic characters of these shells from the specimens I have examined. 
They form the group equirostres of Murchison, Verneuil, and Keyserling, in their section of “ Abnormal 
Spirifers,” and the genus sorhynchus of King. Neither Pander nor these latter writers have described the 
hinge, nor internal characters fully, but the group is obviously a very peculiar one, remarkable for the two 
long, slightly diverging dental lamellz in each valve, and is, I think, most allied to Orthis, an opinion in 
which Murchison, Verneuil, and Keyserling, seem to coincide, though placing them among the Spirifers. 
PORAMBONITES INTERCEDENS (Pand.) 
Ref. and Syn. = Porambonites alta + elevata + pentagona + lata + plana + trigona + subrecta + latissima + parva 
+ rotunda + intercedens. Pander Beit. zur Geogn. = Spirifer porambonites Von Buch. M. V. K. Geol. Russ. 
t. 2. f. 3, 4; 5. 
Sp. Ch —Subpentagonal, depressed, greatest width about the middle of the length, sides elliptically 
rounded; greatest depth rather behind the middle of the shell; entering valve about one-third deeper than 
the receiving one, rostral portions tumid, gradually becoming compressed towards the margin ; beaks very 
small, obtuse; apical angle about 120°; cardinal area very small; hinge-line short, forming a very obtuse 
angle with the lateral margins; lateral margins slightly sigmoid; front margin very abruptly raised into a 
rotundato-quadrate sinus, producing a wide, flat, abruptly defined mesial depression in the receiving valve 
searcely extending within six lines of the beak; mesial ridge of the entering valve scarcely perceptible ; 
surface marked with close, flattened, subequal, longitudinal strize (about eleven in the space of one line at 
the margin), separated by rather narrower sulci, very coarsely pitted. Width of large specimen one inch 
five lines, proportional length %, depth =; . 
Although perfectly agreeing with Murchison, de Verneuil, and Keyserling, that all the above specific 
names of Pander belong to one variable species, I do not think it desirable to add to the number, as they 
have done, by adopting Von Buch’s name, Spirifer porambonites. 1 have used for the species the first 
specific name out of the synonyms used by Pander in his descriptions, although it is rather with the 
large depressed varieties named by him P. pentagona that our specimens have most analogy. It is very 
interesting to find this species in Great Britain, from its apparently very restricted geographical range, 
though occurring in such great profusion in the Lower Silurian strata about St Petersburg, and rarely 
in strata of same age at Christiania. 
Position and Locality ——Not very uncommon in the limestone of Wrae Quarry, Upper Tweed, near 
Broughton. 
Genus. ORTHIS (Dalman.) 
Gen. Char.—Subquadrate, or rounded; hinge-line generally less than the width of the shell; each 
valve has a triangular cardinal area, and mesial triangular foramen open, in the receiving valve, closed in the 
other by its own prominent, bifid, rostral tooth; the receiving valve is the largest, and also is usually the 
most elevated, and gibbous in the middle; opposite valve usually smaller, less convex, and generally with 
a mesial sinus; surface generally marked with longitudinal striz or plaits; shell-tissue closely and very 
minutely punctured; interior surface of receiving valve with a short mesial septum, and a strong diverging 
hinge-tooth on each side, from which a semicircular dental plate extends, on the inside of which is often 
seen a large radiated muscular impression ; entering valve with a prominent, small, bi- or tri-fid rostral 
