BRAOCHTIOPODA. 863 
lamelle are fringed with rather long, irregularly set spinules 
directed toward the commissure of the valves. There are no 
spinules elsewhere on the brachidium. 
Fie. 498. Fie. 499. 
Centronella (Harttina) Anna, Hartt. 
Dorsal and profile views of a preparation of the brachidium ; showing the hinge-plate, broad 
jugal processes, fimbriated descending lamell, l-ng recurved lamellse, ani prominent median 
septum in the brachial valve. 
Type, Harttina Anna, Hartt (sp.). 
Distribution. Carboniferous. 
Dielasma, King. 1859. 
(Plate 52, figs. 10-25.) 
Synonym; “pithyris, King (not Phillips), 1850. 
Shells biconvex ; outline usually elongate-oval; frequently a 
median sinus, with or without a plication at the bottom of it, is 
developed in both valves. 
The apex of the pedicle-valve is closely incurved, so that in 
adult shells but little remains of the deltidial plates. The fora- 
men is large, quite generally encroaching upon the umbo and 
often becoming very oblique to the longitudinal axis; with the 
increase of this obliquity the deltidial plates are thickened on 
their inner surface, which thus becomes more or less protruded. 
The inverted sheath or collar within the foramen is highly devel- 
oped and clearly shown on internal casts. On the interior the 
dental plates are conspicuous, and stand vertically upon the 
bottom of the valve, not showing the convergence and often 
actual union occurring in CRYPTONELLA. 
115 
