546 Forty-fifth Report on the State Museum. 



Subgenus Dignomia, Hall. 1871. 



(Plate 1, figs. 12, 13.) 



Shells with broad, flat median ridge and lateral, sub-marginal 



parietal grooves in the pedicle-valve, a more conspicuous median 



ridge in the brachial valve, with submarginal, diverging ridges 



corresponding to the grooves of the opposite valve. 



Type, Dignomia alveata, Hall. Hamilton group (Devonian). 



Subgenus Glossina, Phillips. 1848. 

 (Plate 1, figs. 10, 11.) 

 Outlines subtrigonal; beaks acuminate. Internal markings 

 obscure. 



Type, Glossina attenuata, Sowerby (Sp.). 

 Distribution. Lower Silurian— Devonian (?)« 



Barroisella, Hall. Ib92. 

 (Plate 1, figs. 14, 15.) 

 Shell externally as in Linguxa. The pedicle-valve bears a high 

 cardinal area, which is a thickened triangular plate divided by a 

 broad pedicle-groove. On the basal margin of the cardinal area, 

 at the angles made by the lateral margins of the pedicle-groove, 

 is a pair of bosses or condyles, which have served either as mus- 

 cular fulcra, or, to some extent, as points of articulation with the 

 opposite valve. The interior of the pedicle-valve bears a sub- 

 quadrate depressed area lying directly beneath, and almost in 

 continuation of the pedicle-groove ; this may represent the 

 umbonal muscular scar. From its ante-lateral angles diverge 

 two sharply defined, linear depressions, which extend about one- 

 fourth the length of the shell, and end abruptly. From outside 

 and behind the extremities of these depressions, begins a pair of 

 long, curved furrows, composed of two shorter curves, the pos- 

 terior rounding over the extremities of the linear depressions 

 referred to, the anterior and longer curves gradually approxi- 

 mating and nearly meeting at a point about one-third the shell's 

 length from the anterior margin. These furrows are accom- 

 panied by low ridges along their inner margin. A low median 

 ridge, with elevated edges, begins at the posterior umbonal 

 impression, and continues to the center of the valve, widening 

 near its anterior extremity. Just behind its termination is a pair 

 of small, usually indistinct muscular impressions, probably the 

 scars of the central muscles. 



98 



