214 BRITISH FOSSIL TRIGONI.E. 



the border of the valve, which there exhibits no appearance of a carinal area or 

 escutcheon. 



Genus — Myophoria. Bronn, 1835. 



Before concluding the present Monograph I was tempted to depart so far from its 

 scope and intention as to refer to a genus, and single British species, allied to Trigonia, 

 and constituting its immediate precursor. Myophoria, a genus of Conchifera special to 

 the Trias, established by Bronn in 1835, has been amply illustrated in his 'Lethsea 

 Geognostica,' and by Goldfuss in his ' Petrefacta Germanise,' including several species of 

 Myojihoria from the Muschelkalk, which the latter author assigned to Trigonia {Lyrodon). 

 In Germany and the Tyrol the Myophoria occur in the Hallstadt, the St.-Cassian, and 

 the Kossen or Rhaetic rocks, important fossiliferous formations, which in Britain are 

 represented only by the Penarth beds, the highest stage of the Trias, and reduced 

 considerably in thickness. At the base of the Lower Lias are certain brown sandstones, 

 grey or greenish marls, black clays, and shales, with occasional limestone bands, having 

 a thickness of from 30 to 100 feet, containing a very characteristic series of Rhsetic 

 fossils, more or less exposed at nuuierous localities, in the long course of the Lias 

 between Somerset and North Yorkshire, probably extending uninterruptedly, but chiefly 

 concealed in its course through the intervening counties. 



The specimens of Myophoria herewith figured represent selected examples of the only 

 recorded British species of that genus, obtained by my friend, Mr. C. Moore, in a bed of 

 hard limestone one foot in thickness, called the " flinty bed of Bere Crowcombe," 

 disclosed by a section made by a canal tunnel at an obscure locality near the town of 

 Ilminster ; the blocks of limestone also contained a considerable series of Gasteropoda 

 and Conchifera included in Mr. Moore's collection of Rhsetic fossils from the County of 

 Somerset, described and figured by him in the Meuioir subsequently cited. 



Myophoria differs as a genus from Trigonia chiefly in the absence of transverse 

 sulcations upon the diverging hinge-processes, and not less universally by the direction 

 of the umbones, which, unlike those in Trigonia, are turned forwards as in the 

 Conchifera generally. 



Limited stratigraphically to the Trias, this genus of small Conchifers exhibits only a 

 portion of that diversity of aspect, both in groups and species, found in its more important 

 analogue Trigonia ; the species may be arranged into three sectional divisions, succinctly 

 described as follows : 



The first group, trigonal in figure, has one, two, or three large costse or varices 

 diverging from the umbones, which for the most part disappear before reaching the 

 lower border. Examples : Myophoria vulgaris, Bronn, ' Lethsea,' tab. xi, tig. 6 ; Myophoria 



