Weno and Pawpaw Formations 115 



the most common variants are here figured. 



Form elevated ; outline angular, broadly truncated and shallowly ex- 

 cavated posteriorly, with a shallow anterior ambital notch, widest just 

 posterior to the antero-lateral ambulacra. The apical system is a little 

 posterior to the center of the test, the distances in front of and behind it 

 having the ratio 10:8. Ambulacra deeply excavated, the unpaired one 

 being longest; the antero-laterals are longer than the postero-laterals (ra- 

 tio 9:7) ; the antero-laterals diverge at an angle of about 105 degrees, the 

 postero-laterals at about 45 degrees. The unpaired ambulacrum is slightly 

 wider than the others. The posterior median keel and the interambulacral 

 areas are elevated, the former being sharp-topped. Peripetalous fascicle 

 visible but irregular. Pores of unpaired ambulacrum short, slit like, 

 oblique, separated by a prominent tubercle. Pores of lateral ambulacra 

 elongate transverse slits which are nearly equal in the forward and the 

 rear zones. Peristome elongated transversely, with a prominent thick- 

 ened posterior lip; periproct high, vertically elongate, ovate. The longi- 

 tudinal section is distinctly elevated, posterior slope straight and inclined, 

 anterior slope rounded, the highest point of the test being on the posterior 

 median keel just back of the apical system. 



HORIZON: Weno to Buda formations. 



The Weno marl contains another species which has deeply excavated 

 short ambulacra, much constricted at each end and flared in the middle. 

 These ambulacra are remarkably short and inflated and have a very 

 characteristic appearance. The whole ambulacral system is placed for- 

 wards on the test, the posterior median keel and the interambulacral areas 

 are elevated, she outline is almost circular and non-angular, the form 

 is low, and the anterior median notch is shallow. 



This species has some resemblance to the poorly figured and described 

 species Hemiaster bexari Clark. 



HEMIASTER RIOVISTAE n. sp. 

 PI. 6, fig. 4; PI. 8, figs. 2-3,5 



MEASUREMENTS : (Type) 



Length on mid-line 25.5 



Width 23.5 



Height 14.0 



HORIZON: Top of Weno formation, marl facies. 



LOCALITY: 720 (type locality), one mile southeast of Riovista, 

 Texas, and one-half mile east of the Waco road. 



