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 lU, FIGS. 11-14. 



1862. Discina, Hall. Sixteenth Kept. N. Y. State Cab. Nat. Hist., p. 28. 



1867. Disclna, Hall. Palaeontology of N. Y., vol. iv, p. 23. 



1873. Trematis, Hall. Twenty-third Rept. N. Y. State Mus. Nat Hist., pi. xiii, fig. 20. 



18S6. SeMzobolus, Ulrich. Contributions to Amei'ican Palseontology, vol. i, p. 25, pi. iii, figs. 8 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, he. 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 {loc. 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, ut. cit.), on account of the sharply triangular 



