104 University of Texas Bulletin 



Holectypus planatus does in the Lower Washita and Fredericksburg beds. 

 It is scattering in the Weno and Pawpaw formations but more abundant 

 in the echinoid horizon at the base of the marl phase of the Weno forma- 

 tion, in association with Enallaster bravoensis, E. wenoensis, Hemiaster 

 riovistae, Epiaster wenoensis, Pedinopsis symmetrica and Holaster. It is 

 sparse in the Mainstreet formation and has a zone of abundance near the 

 base of the Grayson marl. 



HOLASTER sp. aff. SIMPLEX Shumard 



HORIZON: Weno formation, marl facies, abundant near base; Paw- 

 paw formation, marl facies, occasional near top. 



LOCALITIES: 611, 612, 618, 715, 716, 718, near Fort Worth, Texas; 

 721, 722, near Riovista, Texas; cut of Missouri, Kansas and Texas Railway, 

 one mile north of Union Station, Denison, Texas, between localities 605 

 and 606. 



The common Holasters of the Weno and Pawpaw formations have close 

 similarities with the low phase of Holaster simplex Shumard of the Duck 

 Creek and Fort Worth formations, but are specifically distinct. How- 

 ever, it is considered best to defer their description awaiting better ma- 

 terial. These echinoids occur as eroded mud-filled, calcite tests and the 

 ambulacral areas and apical system are almost invariably damaged. 



Tests ovoid in outline, non-angular, anterior notch shallow, longer than 

 tall, greatest perimeter generally above the base. 



Ambulacra flush with surface, postero-laterals in some individuals more 

 divergent than in H. simplex; peristome transverse, oval, lying in a de- 

 pressed space near the ambitus. Peripcroct low, ovoid, vertically elongate 

 lying in tall individuals beneath a prominent posterior median projection. 

 Apical system subcentral elongate. 



It should be borne in mind that the Holasters of the Weno marl are 

 diverse, and that among them Holaster simplex may occur, since its known 

 stratigraphic range extends into the upper Fort Worth limestone. 



The species of Holaster closely related to H. simplex Shumard of the 

 Duck Creek and Fort Worth formations, and found in the Weno and Paw- 

 paw formations shows the same variation in form as the lower species; 

 sloping individuals with their greater perimeter at the base, and top-heavy 

 individuals with the greatest perimeter above the base, are common, the 

 latter being most abundant. This species seems to differ from H. simplex 

 in the shape of the madreporite which is elongate instead of subquadrate 

 and in details of the apical system. Since such species are not easily de- 

 finable by form alone, it has been thought advisable not to describe the 



