Bracutopopa.] LOWER PAL/EOZOIC MOLLUSCA. 193 
nine ribs on the sinus, at six lines or less from the beak, and five to seven in the sinus, the lateral ribs narrow, 
simple, from nine to twelve on each side at five or six lines from the beak. 
This variety is much rarer than the others, but seems to pass gradually into them, though very distinct 
at first sight. 
Position and Locality——Rare in the Bala limestone of Llandeilo, and Bala sandstone of Alt yr Anker, 
Meifod, Montgomeryshire ; a narrow globose variety with only seven or eight large lateral ribs on each side, 
and the six ribs on the mesial fold very narrow, occurs in the limestone of Mathyrafal, S. of Meifod, 
Montgomeryshire. 
Var. 0. SPIRIFERA FISsIcosTaTa (M'Coy). 
Sp. Ch.—General characters of preceding varieties, four ribs on the rostral part of the mesial furrow, the 
two outer of which usuaily branch at four or five lines from the beak, the others branch irregularly lower down 
once or twice ; lateral ribs varying from six to fifteen within three or four lines from the beak, branching irregu- 
larly, some into two, others into four, with age; surface crossed towards the margin with sharp strice of growth. 
This variety does not seem to have been noticed either in Russia or America, yet it is extremely com- 
mon in our old rocks; many of the specimens shew a difference in the muscular impressions in the entering 
valve from the variety /ynz, in having the posterior pair much smaller than the anterior and obliquely elongated, 
so that the division between them and the anterior pair is no longer a horizontal line forming a cross-shaped 
mark ; other specimens, however, more distinctly preserved, seem to have the usual internal characters along 
with the divided ribs. So very variable are the ribs in size and number, that extreme specimens which I haye 
noted, might be referred on the one side apparently to the S. terebratuliformis, (M°Coy), and on the other 
to the S. ovata, (M°Coy). 
Position and Locality——Very common in the Bala schists of Bryn Melyn, Bala, Merionethshire ; schists 
of Peniarth, Meifod, Montgomeryshire; Bala sandstone of Alt yr Anker, Meifod, Montgomeryshire ; Bala 
schists of Gelli Grin, Bala, Merionethshire; impure Bala limestone of Ravenstone Dale, Westmoreland ; 
Coniston or Bala limestone of Coniston Water Head, N. Lancashire; calcareous (Upper Bala) flags of Ash 
Gill, Westmoreland ; schists of Blain y Cwm, W. of Nantyr, Glyn Ceiriog, S. of Llangollen, Denbighshire ; 
schists of Maes Hir, N. E. of Aber Hirnant, N. Wales; impure Bala limestone of Mathyrafal, S. of Meifod, 
Montgomeryshire ; impure limestone of Tyn y Cabled; schists at Bala, Merionethshire ; schists, Aber Hirnant, 
E. of Bala, N. Wales. 
SPIRIFERA CRISPA (Linn. Sp.) 
Ref. and Syn.= Anomia crispa Linn. Syst. Nat. ; Spirifer id. Sil. Syst. t.12. f.8; Bull. Géol. Soc. de France, 
2nd Series, Vol. V. t. 3. f. 42. 
Sp. Ch—Transversely oval, gibbous, cardinal angles broadly rounded, hinge-line rather shorter than 
the width of the shell; cardinal area triangular, varying from one-fourth to nearly one-third the length of 
the hinge-line in height; entering valve with a rounded mesial ridge, not exceeding in size or prominence the 
adjoining lateral ridges, which are broadly rounded, and either two or occasionally three on each side; mesial 
sulcus of receiving valve corresponding to the opposite ridge, and not indenting the lateral margin more than 
the lateral sulci; surface crossed by sharp, concentric, regular amine of growth. Average width four lines, 
proportional length of entering valve ,;;, proportional length of receiving valve %, depth of both valves ™. 
Position and Locality.—Common in the limestone of Clungunford, Shropshire; schists near Llangollen, 
Denbighshire ; schists of Keeper’s Lodge, Goldengrove, Llandeilo. 
SPIRIFERA CYRTAINA (Dal. Sp.) 
Ref. and Syn.= Delthyris cyrtena Dal. Acad. Holm. 1827. t. 3. f. 4. 
Hisinger, Pet. Suec. p. 73. t. 21. f. 4. =? Spirifer interlineatus Sil. Syst. t. 6. f. 6. 
Sp. Ch—Rhomboidal, very gibbous, particularly the receiving valve which is strongly arched, towards the 
large, gently incurveg@ beak ; hinge-line rather less than the width of the shell; cardinal angles obtuse ; cardinal 
[wasc, 11.] Co 
