DESCRIPTIONS OF SPECIES. 429 



examples in being" more contracted at the hinge line and in having the anterior ear 

 more clearly defined. In the sjaionymy of this form probably belongs Pseudomo 

 not is radialis Phillips? of Meek, and possibly also Avicula speluncularia Geinitz, 

 as suggested by Meek. 



Some of the figures given by Meek and Worthen of a form which they referred 

 to Placimopsis vfith the specific name P. carionaria" so much resemble Beede's figures 

 of Paiindonwnotis kmi-sasensis as to suggest that the former species is generically, if 

 not specifically, related to the latter. I am unable to make direct comparisons with 

 specimens, as the Illinois form is not represented in our collections. 



Locality and Iwrizon. — San Juan reg'ion (station 2-34:2); Rico formation. 



PSEUDOMONOTIS sp. 



This species is represented primarily by a specimen of medium size and preser 

 vation from Marguerite Creek (station 2344) in the Rico formation, but to it I have 

 also referred two smaller and less perfect examples from two other stations in the 

 same formation. 



In shape this shell uuich resembles the form which Beede described as Pseudo- 

 monotis hawni var. equlstriata and figured on pi. 14 of his report.* It is a narrow, 

 elongate species, having a length of about 19 mm. and a transverse diameter at the 

 widest point of about 15 mm. At the hinge line the width is 10 mm. 



The posterior ear is flattened and scarcely distinguished by a gentle sinuosity in 

 the outline. The anterior ear is rather inflated and it is defined by a very distinct 

 emargination or notch. The posterior outline is nearly straight in its upper portion, 

 which meets the hinge line at a slightly obtuse angle. It has a gentle' outward curve 

 below, and the inferior outline is strongly rounded. The anterior outline is withdrawn 

 into a well-marked sinus beneath the anterior ear. The shell is rather strongly 

 inflated. 



The surface is marked by a number of moderately distinct wrinkles of growth. 

 The ribs are very obscure, somewhat alternating in size, and not distributed with 

 precise regulai'it}-. There are S or 9 in the space of 5 mm. 



The foregoing description is derived from the large example already mentioned. 

 The two other specimens are' much smaller and much less jierfect. Their length is 

 slightly over 10 mm. The shape, as well as it can be determined, is similar to that 

 of the larger example whose description has just been given. The surface seems to 

 be without radial ribs. 



The nearly obsolete character of the surface ornamentation in these specimens 

 might seem to indicate that they are right valves, but the shape and strong convexity 



tiGeol. Surv. Illinois, Rept., vol. 5, 1873, pi. 27, flg.s. 2b and 2d. 

 6 Univ. Geo!. Surv. Kansas, Kept,, vol. 6, 1900, p. 134, pi. 14, flg. 3. 



