PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 741 
feature of Taphrodonta is thus its interior characters. Inside the pedicle valve 
the dental plates and articulatory apparatus are like those of Palaeostrophomena 
and other Plectambonitacea. The muscle field is rather generalized and without 
septa, at least in this species. Perhaps the most distinctive feature of the interior 
of the pedicle valve is the thickening of the flanks of the shell on each side of 
the median sulcus and posterior to the margin. This makes a raised or thickened 
visceral area but a thin marginal zone. The latter evidently fits closely to the 
thickened marginal zone of the brachial valve. The anterior shallow marginal 
area is strongly pustulose. 
The most striking feature of the brachial valve interior is the long median 
ridge consisting of 2, or what appear to be 2, septa welded together to make a 
broad ridge with an elevated margin on each side. This ridge is joined to the 
notothyrial platform which carries a thin blade for a cardinal process. The 
brachiophores are moderately long, their proximal ends buried in the tissue of 
the notothyrial platform. Where the brachiophore protrudes from this tissue 
it is thickened on the outside, the boss thus produced undoubtedly sharing in 
the articulation of the valves. The distal end of the brachiophore is a short, sharp, 
and thin crus like that seen in some orthids such as Hesperorthis. 
Of especial interest in this genus is the marginal region of the brachial valve 
which is considerably thickened and forms a steep slope that fits into the thinned 
marginal area of the pedicle valve. Both areas, the thinned one of the pedicle 
valve and the thickened area of the brachial valve, are strongly pustulose. In 
opening, only a thin passage would result between the valves, the pustules form- 
ing an effective type of strainer. This role for the pustules also may be seen in 
the Productacea where it is developed to perfection. 
The ensemble of characters in this genus are most suggestive of Jsophragma 
which also possesses a median ridge very much like that of Taphrodonta. Despite 
the similarities, strong differences may be detected. In the first place the exterior 
of the two genera is unlike. Jsophragma has a reversed convexity to the brachial 
valve. It is concave in the young but becomes convex anteriorly. In other words 
the convexity is the reverse of that of Taphrodonta. 
Inside the valves other differences may be seen between Taphrodonta and 
Isophragma. The muscle field of the pedicle valve of the latter genus is wide, 
extends to about the middle, and has elongate diductor scars, whereas this feature 
of Taphrodonta is short and narrow. The teeth of Jsophragma seem to be more 
simply constructed. Inside the brachial valve the median ridge shows its dual 
origin more strongly in Isophragma than in Taphrodonta. Furthermore, the 
brachiophores of Isophragma are short, flat blades and the cardinal process, 
although simple, is inclined to be bulbous. 
TAPHRODONTA PARALLELA Cooper, new species 
Plate 165, A, figures 1-22 
Small, semielliptical in outline with the hinge forming the widest part ; cardinal 
extremities acutely pointed; sides moderately oblique, slightly rounded ; anterior 
