BRACHIOPODA. 105 



Observations. These shells differ IVom Achotreta 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 (t\vo 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'-, Maitiiew. Illn.stration,s of the Fauna of i\u'. St. .Jcilm Gi-oup, 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, ai'e 

 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 DisciNorsis. 



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, fig-. 1 6. 



t Systdme Silurien Boheme, vol. v, pi. 95, tig. vii. 1879. 



