142 PALEONTOLOGY OF NEW YORK. 



and T. corona, Salter ; T. canccllata, Sowerby, does not appear in the catalogue), 

 is meager and extremely unsatisfactory, though we may assume that the un- 

 certainty in regard to these points will soon be cleared away. Barrande's 

 Trematis Bohemica* is unquestionably a Dinoeolus. At present we are able to 

 recognize eleven species as undoubtedly congeneric, in addition to which are three 

 of questionable alhnity which are little known. All these are confined to the 

 Trenton and Hudson faunas of the Silurian, and the earliest to appear is 

 Billings' T. Huronensis, from the Black River limestone. 



The list of species is as follows : 



Trematis terminalis, Emmons. Trematis quincuncialis. Miller and Dyer. 



Trematis Montrealensis, Billings. Trematis umbonata, Ulrich. 



Trematis Ottawensis, Billings. Trematis fragilis, Ulrich. 



Trematis Huronensis, Billings. Trematis ohlata, Ulrich. 



Trematis millepundata. Hall. .'' Trematis pustulosa. Hall. 



Trematis punciostriata. Hall. ?? Trematis rudis,'iia\\,==ScEi'£OCR\mA{'.). 



Trematis crassipunda, Ulrich. .■'.'' Trematis Dyeri, Miller. 



Genus SCHIZOCRANIA, Hall and Whitkield. 1875. 



PLATE IV G, FIGS. il-Sn. 



1847. Orbicida, Hall. Palseontology N. Y., vol. i, j). 9i), pi. Ixxx, fig-s. 9 a-d. 



1863. Trematis, Billings. Rept. Progress Canadian Geological Survey, p. 159, fig. 126. 



1873. Treiiiatli, Hall. Tweiity-lliird Rept. N. Y. State Cab. Nat. Hist.. Expl. pi. xiii, tigs. 21, 22. 



1875. i^chizovrania. Hall and Whitfield. Geol. Ohio ; PaiEeont., vol. ii, p. 73, pi. i, tigs. 21, 22. 



(!) 1878. Treinat'is (Schizocranla), Barrett. Ann. New York Academy of Sciences. 



1884. (Discinocai-isf), Davidson. General Sunini;iry of the British Brachiopoda, p. 3.")2. 



Diagnosis. Shells sub-circular in outline, inequivalve, unarticulated. Pedi- 

 cle-valve flat or concave ; apex subcentral. A deep triangular notch extends 

 from just behind the beak to the margin, where its arc is equal to about one- 

 sixth of the periphery. The apex of this broad pedicle-notch is occupied by a 

 triangular transverse plate varying in size with the age of the shell, but ex- 

 tending for one-fourth to one-third the length of the opening. Surface marked 

 by concentric growth-lines. On the interior no muscular impressions are vis- 



* Syst. Sil. Boheme, vol. v, pi. 94, fig. vi. 1879. 



