DESCRIPTIONS OF SPECIES. 431 



1894. Monoptera longispina. Keyes, Missouri Geol. Surv., vol. 5, p. 114, pi. 43, fig. 1. 



Upper Coal Measures: Kansas City, Mo. 

 1900. Limopteria longispina. Beede, Univ. Geol. Surv. Kansas, Kept., vol. 6, p. 127, pi. 16, fig. 6. 



Upper Coal Measures: Kansas City, Turner, Lawrence, Kans. 



The form which I have referred to Monopteria longispina has been found only in 

 the Rico formation, and it is represented at station 2341 (Scotch Creek) by two very 

 imperfect specimens. The accuracy of the identification is qualified bj^ the character 

 of the material. 



The strong-h' curved umbonal ridge and prolonged posterior portion of this form 

 give it a shape much resembling that of M. marian and M. longispina, but the 

 retracted anterior margin would prevent its I'eference to the first-named species. 



LocaUty and horizon. — San Juan region (station 2341); Rico formation. 



MoNOPTEKiA ALATA Beede. 



PL IX, fig. 3. 



1898. Monopteria ffibbosa alata. Beede, Kansas Univ. Quart., vol. 7, p. 189, fig. 5. 

 1900. Limopteria alata. Beede, Univ. Geol. Surv. Kansas, Kept., vol. 6, p. 130, pi. 5, fig. 5. 

 Upper Coal Measures: Turner, Lawrence, Kans. 



Shell small, subpentagonal. Hinge line straight, about once and one-half as 

 long as the width below. The bodj^ of the shell is marked by two angulations, the 

 antei'ior one almost perpendicixlar to the hinge line, the other diagonal!}^ dii-ected, 

 nearly bisecting the angle thus formed. The anterior angulation is near the margin 

 of the shell, which falls away very rapidly along this line. The anterior outline, 

 therefore, is subrectilinear and is inclined to the hinge line at but little more than a 

 right angle. An abrupt curve connects it with the inferior outline, which is also 

 subrectilinear and nearly parallel to the hinge line. Where it intersects the diago- 

 nal angulation there is another sharp turn to a direction nearly normal to that which 

 it had formally been pursuing. Continuing thus for a short distance it begins to 

 assume a backward course, and, with a sigmoid curve, joins the superior outline. 

 The posterior alation thus formed is strong, but broad and blunt. The surface is 

 marked by numerous fine, regular, sublamellose striae, crowded in the upper regions 

 of the shell, but becoming spaced peripherally. The description just given is drawn 

 up from the onlj^ specimen which has thus far been found. The fact that the body 

 of the shell in this form is short and nearly erect instead of bending backward into a 

 direction more or less parallel with the hinge line, distinguishes it from If. longis- 

 pina and M. marian, and also to a less degree from 3f. subalaia and M. gihbosa, and 

 allies it more especially with M. alata and M. polita. I at one time regarded this 

 form as representing a new variety subordinate to M. polita, but now feel that it 

 should not be distinguished from M. alata. Although it is true that certain diflfer- 



