MEXICAil BOIINDARY LINE. 145 



Fig. la. Upper side of specimen. 



Fig. lb. Lower side. 



Fig. Ic. Posterior view. 



Fig. Id. Portion of the summit enlarged. 



Locality. — Leon Springs, El Paso road. 



TOXASTER TEXANUS. 



Plate I, Fig. 2, a-c. 



Toxaster Texanus, Roemer, Kreidebildungen von Texas ; p. 85, pi. x, fig. 3. 



Shell oblong, subpentagonal-ovate, rotund before, the middle emarginate, truncate behind, 

 elevated convex ; mouth transverse, subreniform ; anal aperture round-oval ; the larger tuber- 

 cles arranged in a triangular area upon the lower surface. 



The specimens of this species in the collection are somewhat compressed vertically, cordate- 

 ovate in form, rather abruptly emarginate in front. 



Fig. 2a. View of the base of a specimen. 



Fig. 26. Upper side of the same. 



Fig. 2c. Posterior view. 



Locality. — Leon Springs, Texas. 



CYPHOSOMA TEXANUM. 



Plate I, Fig. 3, a-c. 



Diadema Texanum, F. Roemer, Texas ; p. 392. 



Cypliosoma Texanum, Roemer, Kreidebildungen von Texas ; p. 82, pi. x, fig. 6. 



Orbicular, scarcely subangular, little elevated, depressed above, plane or concave below ; 

 tubercles of the ambulacral and interambulacral areas equal, distinctly crenulate ; tubercles of 

 the ambulacral areas biserial, intermediate tubercles few ; tubercles of the interambulacral areas 

 arranged in two principal series, and two slightly smaller accessory series, intermediate tubercles 

 numerous, scattered. 



The specimens of this species in the Boundary collections are fragmentary. 



Fig. 3a. Profile view. 



Fig. 36. View of lower side. 



Fig. 3c. Enlargement of surface, showing the ambulacral and interambulacral tubercles, 

 pores, etc. 



Locality. — Leon Springs, Texas. 



HOLECTYPUS PLANATUS. 



Plate I, Fia. 4, a, h, c, d, e,f. 



Orbicular or subpentagonal, moderately elevated, extremely depressed conical ; inferior sur- 

 face plane, concave in the middle ; ambulacral areas somewhat prominent above the rest of the 

 surface ; tubercles small above, larger below, vent ovate, very large, reaching from the mouth 

 to the margin. 



19 M 



