BRACHIOPODA. 
105 
Observations. These shells differ from Acrotreta in their less distinctly 
defined posterior area and in the character of their internal markings. The 
apical callosity is much more prominently developed and the ridges radiating 
from it (two in Acrotreta, according to Walcott*) more numerous. The lack 
of definition in the posterior subapical slope, apparent in the young shells from 
the Utica horizon at Covington and the Trenton limestone at Trenton Falls, 
suggests the condition of this feature in the genus Mesotreta, and also in the 
species figured by M. Barrande,! from the Etage D, under the name, Acrotreta 
Babel , which has an elevated, conical pedicle-valve with a perforated apex and 
unspecialized posterior slope. 
Genus DISCINOPSIS, gen. nov. (Matthew). 
PLATE m, FIGS. 20-24. 
1885. Acrotreta?, Matthew. Illustrations of the Fauna of the St. John Group, No. vi, p. 37. 
From the examination of the original specimens of Mr. Matthew’s species, 
Acrotreta ? Gulielmi, from the St. John group, at Portland, N B., it has become 
evident that the internal impressions, especially those of the perforated valve, are 
of a character widely different from those of Acrotreta, or, indeed, of any of 
the allied genera. Upon expressing this conviction to Mr. Matthew with the 
request for any additional material that might throw light on this rather 
obscure shell, he kindly placed at our disposal all his specimens of the species, 
and in accordance with our suggestion that it represented a new generic form 
and would hence require a new name, has proposed for it the term Discinopsis. 
Diagnosis. Shell subcircular in outline. Surface depressed-conical, apices 
excentric, not marginal. Pedicle-valve with the apex truncated by a circular 
foraminal aperture (?). The interior of this valve is characterized by a pair of 
deep, diverging furrows, passing forward from the beak or internal foraminal 
opening, in broad curves which converge toward the anterior margin but without 
meeting. These furrows enclose a thickened and somewhat elevated central 
area, which, in the subumbonal region is apparently free, projecting for a short 
* Paleontology of the Eureka District, pi. i, tig-. 1 b. 
t Systeme Silurien Boheine, vol. v, pi. 95, fig. vii. 1879. 
