Bracuropopa. | UPPER PALOZOIC MOLLUSCA. 415 
in the depth occurred in the very transverse forms. Some of the specimens from Gera shew as many as three 
obsoletely marked ribs in the mesial sinus, more usually however there is only one or none. 
Var. a. Length about two-thirds the width; anterior lateral margins strongly convex. 
Var. 8. Nearly three times wider than long; lateral margins nearly straight or slightly concave 
(gradually passing into a). 
Position and Locality—Common in the Magnesian limestone of Humbleton. 
SPIRIFERA CRISTATA (Schlot. Sp.) 
Ref. and Syn.= Terebratulites cristatus Schl. Akad. Miinchen, Vol. VI. t. 1. f. 3 = Trigonotreta id. King, 
Perm. Foss. t. 8. f. 9 to 14. 
Desc.—Entering valve nearly semicircular, moderately gibbous: hinge-line seareely as long as the shell is 
wide; cardinal angles obtuse; receiving valve very gibbous; beak large, only moderately incurved ; profile 
regularly arched, so that the greatest depth is at about the middle of the length ; cardinal area very large, 
slightly curved, triangular, height one-third of the width; triangular opening about one-third higher than wide, 
closed nearly to the base by a prominent convex pseudo-deltidium ; cardinal area of entering valve very small ; 
surface of both valves very deeply undulated by about eight very large, angular, simple, deeply separated ridges, 
the middle pair on the receiving valve, and middle one of the entering valve distinctly larger than the others ; 
surface crossed at very irregular distances by strong imbricating laminze of growth, which seem undulated by 
crossing over the ridges; under a lens of three quarters of an inch focus, surface with very coarse, rather 
distant, granular punctures ; casts shew a mesial septum in each valve, a little longer than the diverging dental 
lamellze. Width six lines, proportional length of receiving valve =, of entering valve 5%, depth of receiving 
valve +, depth of entering valve =. 
I have seen the spires of this species, which are of moderate size; the very coarse granular punctures 
occasionally seen, more than half their diameter apart. Professor King mentions that the only difference he 
could perceive between this species and the S. octoplicata is the greater width of the latter; but I observe that 
specimens of the latter have a proportionally much lower cardinal area, longer hinge-line, are of nearly double 
the average size, and have five or six lateral plaits on each side of the mesial sinus, which are comparatively so 
small that at the margin three of them would be required to equal the mesial ridge in width, while in the present 
species the mesial_ridge is little wider than the adjoining lateral ones. ‘The carboniferous Spirifera inseulpta 
(Phill.) seems also to him to be undistinguishable from the Permian S. cristata ; but besides the greater height 
of the cardinal area, I have never seen more than one or two lateral ribs on each side of the median one, and 
the punctation seems slightly closer. Many decomposing specimens present the strange appearance noticed by 
Professor King of the substance of the shell falling away from the surface of the cast, leaving the latter covered 
with vertical, short, cylindrical spines, which are casts of the punctures which passed through the substance of 
the valves. 
Position and Locality.—Not uncommon in the Permian limestone of Humbleton. 
SPIRIFERA DUPLICICOSTA (Phill.) 
Ref. and Syn. =1d. id. Phill. Geol. York. Vol. II. t. 10. f. 1; +S. (Brachythyris) planicostata M°Coy, Synop. 
Carb. Foss. Irel. t. 21. f. 5; $+ (var. a) S. crassa de Kon. Anim. Foss. Bel. t. 15 bis. f. 5; +S. fasciger 
Keyser. Wissenschaft. Beobach. Petschora Land. t. 8. f. 3, 
Desc.—Transversely oval when old, or obscurely rhomboidal when young; hinge-line rather less than the 
width of the shell, forming obtusely-rounded cardinal angles ; lateral margins nearly horizontal ; front raised into 
a deep sinus, triangular when young, becoming semielliptical or oblong when old. Entering valve gently convex 
when young, and for about half an inch from the beak in old specimens, after which the gently convex sides 
become gradually flattened towards the cardinal angles, and arched downwards on each side of the mesial lobe, 
which is thus left very prominent, and rounded, corresponding with the elevation of the mesial sinus at an angle 
[rasc. 111] 3H 
