Bracuropopa. | UPPER PALAZOZOIC MOLLUSCA. 423 
tures as large as those of a pin, and sometimes with tumid edges, may occasionally be seen at intervals of about 
one-eighth of an inch, both in the sulci and more rarely on the ribs. 
Position and Locality—Both the var. striata and var. attenwata yery common in the carboniferous lime- 
stone of Derbyshire. 
SPIRIFERA SUBROTUNDATA (J/‘Coy). 
Ref. and Syn.=8, rotundatus Sow. Min. Con. t. 461. f. 1. (not of Martin.) 
Desc.—Transversely oblong or quadrato-ovate, moderately depressed ; hinge-line less than the width of 
the shell ; cardinal angles flattened, obtuse ; sides gently convex, acute ; lateral margins horizontal ; middle 
of the front abruptly raised, at rather more than right angles from the plane of the lateral margins, into a 
deep, oblong, or semielliptical sinus; entering valve gently convex in the middle, becoming gradually flattened 
towards the margins; profile gently arched from the beak to one-third the length (half an inch), beyond 
which it is straight to the margin; mesial ridge very strongly defined from the beak by two deep sulci, 
prominent, gently convex or divided by a shallow mesial suleus; each side with about eight broad, convex, 
simple ribs, some of which continue simple, and others dichotomise towards the margins of large specimens, 
where the ribs vary from one to nearly two lines wide in old individuals, there amounting to sometimes 
thirteen, the cardinal angles remaining smooth. Receiving valve very gibbous, most so at one-third from the 
beak, almost regularly arched from thence to the middle of the front sinus; mesial hollow very deep, wide, 
flattened, distinctly defined from the beak, and containing two obscure ribs, slightly smaller than the lateral 
ones, on each side of a flattened mesial space, slightly broader ‘than one rib; cardinal area narrow; beak 
moderate, approaching that of the entering valve. Average width two inches six lines, proportional length 
of receiving valve varying from = to =, length of entering valve %, depth of entering valve 2, depth of 
receiving valve ; to ;3, width of front sinus 5, depth of ditto *%, width of hinge-line 7%, width of cardinal 
area ;; young specimen one inch wide, length of receiving valve *, depth of both valves %. 
The lateral radiations of this species are broad and flattened when well preserved, and vary greatly in width 
at margins of old specimens, according to whether the primary ridges remain simple or bifureate. I regret 
that in my old volume on the carboniferous limestone fossils of Ireland (in which I pointed out that the Spirifera 
rotundata of Phillips and Sowerby was not the true votwndata of Martin, which was figured by Phillips under 
the specific name planata) I did not give a separate name to this species, which by its broad, smooth, mesial 
ridge, deep sinus in the front margin, greater gibbosity, &c. is very distinct from the original rotwndata of 
Martin. Public opinion has since so strongly increased in favour of priority, that I no longer hesitate to do so. 
The depression of the sides or sharpness of the margins from the acute angle at which the valves meet each 
other, less gibbosity and greater proportional width, distinguish specimens of all sizes from the little Spirifer 
pinguis of Sowerby, with which in other characters it is identical. 
Position and Locality —Common in the carboniferous limestone of Bolland. 
SPIRIFERA TRIGONALIS (Mart. Sp.) 
Of this very common species there are several varieties, which I shall describe separately. 
Var. a. TRIGONALIS (Mart. Sp.) 
Ref. and Syn.= Anomites trigonalis Mart. Pet. Derb. t. 36. f. 1.=Spirifer id. de Koninck, Anim. Foss. Bel. 
t.17. f. 1. + S. striatus id. id. (not of Martin) t. 16. f. 3.+ 8. Strangwaysi M. V. K. Geol. Russ. t. 6. 
f.1.+8. incrassatus Hichw. Sp. M. V. K. Geol. Russ. t. 6. f. 3.+8. Pentlandi VOrb, Voy. dans 
PAmér. Mér, p. Pal. t. 5. £.15.+8. rhomboidea Phill. Geol. York. t. 9. £.8,9; 2+. Hischerianus de 
Kon. Foss. Bel. t. 14. f. 3. 
Dese—Subrhomboidal, gibbous ; hinge-line exceeding the width of the shell, forming cardinal angles of 
variable acuteness; receiving valve moderately gibbous, greatest depth at one-third from the beak, from which 
[rasc. 11.] 31 
