WHITE.] PALEONTOLOGY — CRETACEOUS FOSSILS. 281 



" I have not yet seen the hinge of this shell, or its left* [right] valve, 

 and therefore have some doubts in regard to which of the sections of the 

 old genus Avicula it would most properly fall into. If the right valve 

 is (as I am incUned to think the case) nearly flat, with a deep, sharply 

 cut byssal sinus, and its beak not distinct from the hinge-margin, it will 

 probably fall into a little group for which I some time back projjosed 

 the name Oxytoma, ty[)ified by Avicula Munsteri Bronn. It dillers re- 

 markably from typical species of Avicula in its erect form, its mnbonal 

 axis being inclined a little backward instead of strongly forward. From 

 Pseudomonotis, with which it agrees in its erect form, and the elevated, 

 strongly incurved beak of its right [left] valve, it differs very strongly 

 in having decided, well-develoi)ed ears, both in front and behind. Dr. 

 Stoliczska thinks the characters of the genus Pseudomonotis should be 

 extended so as to include Oxytoma. Should this view prevail, the name 

 of our species would probably become Pseudomonotis ( Oxytoma) gastrodes. 

 It seems to me, however, that Oxytoma stands more nearly related to 

 Avicula proper than to Pseudomonotis^ as tyi)ifled by the Permian species 

 P. spelun^aria, so that if we unite Oxytoma to Pseudomonotis, I cannot 

 see why we might not, on the same principle, take another step of the 

 kind and restore both to Avicula, which I am certainly not inclined to 

 do, though I regard Oxytoma as a subgenus under Avicula. 



" I use the name Avicula here, as elsewhere, subject to the change 

 that it is probable the ndes of nomenclature will demand in the restora- 

 tion of the older name Pteria, which woukl require the name of our 

 species to be WTitten Pteria gastrodes, if it falls into that group." 



Subgenus Pseudoptera Meek. 



Pteria (Pseudoptera) propleura Meek. 



Plate X, figs. 2 a and. h, and c. 



Avicula {Pseudoptera) propleura MEEk, 1873, An. Eej). U. S. Geol. Siirv. Terr, for 1872, 



p. 489. 

 Avicula {Pseudoptera) rhytophoraMEEk, 1873, An. Eep. U. S. Geol. Surv. Terr, for 1872, 



p. 490. 



After careful examination, not only of all Mr. Meek's tyi^e-specimens, 

 which were all found associated in the same stratum, but also others 

 which I have collected at the original locality at Coalville, Utah, I am 

 satisfied that both this species and the form which he described in the 

 same publication under the name of Avicula [Pseudoptera) rhyto2)hora Sive 

 specifically identical. I therefore refer both forms to Pteria {Pseudoptera) 

 propleura, which name comes first in order in the volume above cited ; 

 but I herewith give his description of both forms, together with his 

 remarks upon the same, and also figures of Mr. Meek's types of both 

 forms on plate x : 



" Shell, as determiued from a left valve, obliquely ovate-subtrigonal, 

 moderately convex along the oblique umbonal slope in front of the middle, 

 and comi)ressed-cuneate behind 5 i)Osterior margin with its general out- 

 line nearly vertical and slightly straightened along the middle, thence 

 extending obliquely upward and a little forward, with a very faint sin- 

 uosity above, to the hinge, which it meets at an obtuse angle, while it 

 rounds rather abruptly into the more or less rounded base below ; ante- 

 rior margin ranging obliquely backward and do^Miward nearly parallel 



*Doubtles3 au inadvertent error. His example is a left valve, wMch he describes 

 as such. 



