HEEDE: new forms of PSEUDOxMONOTIS. 83 



does from P. Jiaiinii (in a different degree) in its posterior margin, 

 development of the ears, surface markings and flatness of the beak. 

 The study of large collections from the same intervening horizons 

 may prove the two inseparable. If it is true that all the known 

 forms of the genus do completely intergrade, I think that certain 

 extreme forms will still have to be distinguished as varieties or 

 species, though this may not apply to the particular shell under 

 consideration. It is easily distinguished from the two shells just 

 described, but is very closely related to the one follovving, and 

 indeed may be the the same, though I think not. 



Pseudomonotis Cf. ha-wni Meek, Pal. Upp. Mo., p. 54, pi. ii, fig. 53-0, 



This is one of the most varied and puzzling shells in the Coal 

 Measures of the west. Occasionall}' one is found that approaches 

 F. Iiawni very closely, while on the other hand some are found 

 which resemble closely in external appearance P. spehincaria or 

 some of its varieties as figured by King (loc. cit. ). 



While it varies greatly in size, outline and markings, there are 

 some characters by which it may be possible to distinguish it from 

 P. Iiawni. Two of the more common forms of this shell are figured 

 on plate XIX ff. i-if. They show some of. the variations in lobing, 

 convexity and general outline. These shells differ, the great 

 majority of them, from P. /laivni, in being much more convex or 

 gibbous, in having a more or less well defined posterior lobe and 

 in being oblique. Most of the specimens of P. kaiviii that have 

 come under my observation have a beak very much more like that 

 of an Azuculopcctcn than have the shells under consideration. In 

 these, the beak is generally more gibbous and less pointed, in 

 some cases hardly distinct from the general swell of the umbo. 



Specimens from the Permian were kindl}- loaned me for com- 

 parison by Professor Charles S. Prosser, and the National Museum 

 through the kindness of Mr. Charles Schuchert. There are also 

 specimens in the collections of the Universit}^ from Grand Summit, 

 Cowley county, Kansas. The shell under consideration differs 

 from nearly all of these in the nature of the beak and, to some 

 extent, the outline and convexity. However, some specimens sent 

 by Professor Prosser, labelled "Neosho formation, Clements, Kan- 

 sas," possess a flat beak and show a tendency toward posterior 

 lobing and consequently approach more closely our Coal Measures 

 shell than P. Iiawni. On the whole I am inclined to think that 

 the shell can be separated varietally from P. Iiawni, though I 

 refrain from doing so at present. I have in my collection speci- 



