234 University of Texas Bulletin 



ited by well marked borders. These margins and the crests of the other 

 interambulacra give the polygonal contour to the figure of the shell. 



The peristome is small and of subpentagonal form. Its position is ex- 

 centric toward the front; the lip is rather prominent. The periproct is 

 not well preserved, but is of oval form and lies in the upper part of the 

 posterior face. The apicial apparatus is relatively large, the two posterior 

 pairs are widely separated from the anterior ones ; the details can not be 

 clearly recognized. 



Dimensions: 



Antero-posterior diameter 27.8 mm. 



Transversal diameter 27.3 mm. 



Height 19.0 mm. 



Distance between the apex and the posterior margin 16.2 mm. 



Our species is not very characteristic but I have not found one with 

 which it might be identified entirely. It resembles to a certain degree 

 Hemiaster Meslei Peron et Gauthier, 1 but in this species the posterior am- 

 bulacra diverge much more than in ours, the contour is more notched in 

 front, the furrow of the impair ambulacra is much narrower and deeper. 



As we have not more than one well preserved individual I only describe 

 and figure it without giving a new name to this species, or identifying it 

 with a known one. 



Number of specimens: 2. 



Age : Upper Cenomanian ( ?) , lower horizon of Cerro del Macho. 



l Cotteau, Peron et Gautheir, Ech, foss. de 1'Algerie IV, p. 102, pi. 2, Igs. 5-8. 



