430 BRITISH PALAZOZOIC FOSSILS. [Bracutopopa. 
the beak; beak large, tumid, narrow, much incurved ; cardinal area low, triangular, no trace of mesial fold ; 
surface of both valves covered with subregular, concentric, obscurely imbricating lamellze (averaging eight in 
three lines near the margin), very obscurely angulated in the middle, the anterior slope of each marked with a 
row of strong, longitudinal, concave notches (averaging fifteen to seventeen in two lines), producing a very 
delicate imperfect reticulation, obscurely distinguishable by the naked eye; posterior slope of each sometimes 
with obscure radiating lines, continued from the narrow intervals, between the notches of the anterior slope. 
88 80 
Average width eleven lines, proportional length of receiving valve ;;,, of entering valve =, length of hinge- 
line 4, height of cardinal area ;;,, depth of entering valve =;, depth of receiving valve ;%, length in some rare 
specimens equalling the width. 
This species, from the peculiar structure of the surface, and the slight divergence of the dental lamelle, 
with their strong mesial septum, was originally combined in my Synopsis (of Carb. Foss.) with the S. imbricata, 
S. reticulata, S. microgemma, &e. into a little group called Reticularia. There is a fine submedial impressed 
line, apparently a fracture, visible in many specimens from the beak to the front margin. 
Position and Locality —Common in the main carboniferous limestone of Derbyshire ; very common in the 
lower carboniferous limestone of Lowick, Northumberland ; common in the dark lower carboniferous limestone, 
Isle of Man; in the dark carboniferous limestone of Craige, near Kilmarnock; very common of small size in 
the carboniferous limestone of Berwick-on-Tweed. 
SprRIFERA (JZartinia) RHOMBOIDALIS (J/°Coy). 
Ref—Id. id. M°Coy, Syn. Carb. Foss. Irel. t. 22. f. 11. 
Dese.—Subrhombiec, gibbous, length and width about equal ; cardinal angles rounded ; cardinal area very 
small, triangular ; beaks small, incurved, approximate ; mesial fold very prominent towards the margin, narrow, 
rounded, or subangulate ; mesial sulcus deep, wide, angular, continued to the beak; sinus in the margin very 
large, abrupt, semielliptical or pointed; surface radiated towards the margin with numerous, obtusely rounded, 
nearly obsolete ridges; tissue under the lens very minutely fibrous. Width about seven lines; proportional 
length of receiving valve #4, of entering valve 7, width of hinge-line im» height of area ;;, depth of sinus 4, 
width thereof *, depth of both valves 7%. 
This species is allied (on a small scale) to the S. protensa Phill., from which it differs in the length being 
equal to the width, and in the very small size of the cardinal area. 
Position and Locality—Rare in the carboniferous limestone of Derbyshire. 
SprriFeRA (Martinia) sumiuis (M/*Coy). 
Ref. and Syn. ?= Spirifera plebia Phill. Pal. Foss. f. 121. (not A. plebia Sow.) 
Desc.—Longitudinally ovato-rhomboidal or subtrigonal, very gibbous ; front narrow, much produced into a 
tongue-shaped elevation ; mesial ridge wide, indistinct except towards the margin of the entering valve; little or 
no mesial hollow in the receiving valve; beaks small, approximate; surface smooth; cardinal area short, 
triangular. Average width ten lines, proportional length of receiving valve ;;, depth of both valves 7%, width of 
cardinal area =. 
I provisionally give this name to a very small species, rarely attaining (even when apparently old) an inch 
in length; it has been taken for the young of Martinia glabra, but is distinguished by its narrow produced 
front, the smallness of its beaks, and the usual want of the mesial sulcus in the larger valve ; it is probably the 
S. plebia (Sow) of Phillips, but is distinguished from the true A. plebia by its cardinal area and hinge-line, Its 
length and traces of lineation on the cast make it very like the young of S. decora, but the narrow area and 
approximate beaks seem to separate it therefrom, while the length and gibbosity separate it from S. symmetrica, 
which it resembles in the beak and cardinal area. If those species should ultimately be found to be varieties of 
one specific type, as suggested, this blending of their characters, with slight differences in the present form, 
would render it very probable that it was a dwarf or young variety of the same. 
