BRACHIOPODA. 
87 
permanent feature of the species and genus (p. 22), it having been observed in 
but a single instance ; but should more complete material establish its persist¬ 
ence it would serve not only as a feature of generic distinction, but would 
remove this form far from the Oboloids (cf. Crania ? Sedgwicki, Lewis: David¬ 
son, British Silurian Brachiopoda, p. 83, pi. viii, fig. 25, which is believed not 
to be a brachiopod). 
SCHIZOBOLUS, Ulrich. 1886. 
PLATE III, FIGS. 11-14. 
1862. Discina, Hall. Sixteenth Rept. N. V. State Cab. Nat. Hist., p. 28. 
1867. Discina, Hall. Palaeontology of N. Y., vol. iv, p. 23. 
1873. Trematis, Hall. Twenty-third Rept. N, Y. State Mas. Nat Hist., pi. xiii, fig. 20. 
1886. Schizobolus, Ulrich. Contributions to American Palaeontology, vol. i, p. 25, pi. iii, figs. 3 a-d. 
Diagnosis. “ Shell oval, depressed-convex, slightly inequivalved ; valves in¬ 
articulate ; structure calcareo-corneous. Cardinal margin somewhat thickened. 
“ Ventral valve with the apex at the terminus of a rather deep notch in the 
posterior margin; interior of the valve with two pairs of adductors, separated 
by a faint median ridge or septum which traverses the valve from the posterior 
margin, where it is bifurcated, to a point about two-thirds the length of the 
valve from the anterior margin. The posterior adductors are very faint. 
“ Dorsal valve with the posterior margin straightened, the apex subterminal 
and but little elevated; interior of valve with a slender median septum which 
separates two pairs of faintly impressed muscular scars; the posterior pair 
large, oval and situated just in front of the cardinal margin, the anterior pair 
are less distinct, smaller, of triangular shape, narrowest in front, and situated 
near the anterior end of the mesial septum. 
“Very faint impressions of lateral muscles were observed near the margin 
of both valves.” (Ulrich, loc. cit .) 
Type, Discina truncata, Hall. 
The type-species of Mr. Ulrich’s genus was described first in 1862, and sub¬ 
sequently, with illustration, in 1867 (toe. cit.), as Discina truncata, from the 
Genesee slate of Seneca county, New York. In both these places attention 
was called to the fact that the muscular impressions, as far as observable, dif¬ 
fered from those of Discina. Subsequently the species was referred to the 
genus Trematis, Sharpe (1873, cit.), on account of the sharply triangular 
