70 MESOZOIC AND CENOZOIC ECHINODERMATA OF THE UNITED STATES. 



Dimensions. — Length 27 millimeters; width 27 millimeters; height 12 millimeters. 



Description. — This typical Echinobrissus is of a moderate size, somewhat depressed above, 

 and subquadrate in marginal outline. The posterior portion is broader than the anterior and 

 distinctly lobed. The base is concave. 



The ambulacra!' areas are narrowly lanceolate, and on the upper surface the poriferous zones 

 are subpetaloidal. The inner rows of pores are round, the outer oval, with acuminated inner 

 margins and obliquely placed. The interambulacral areas are formed of broad plates that bear 

 numerous small perforated and mammillated tubercles. A microscopic granulation covers the 

 miliary space. 



The apical system is small and compact and the perforations of the genital plates distinct. 



The peristome is large, excentric, situated at some distance in front of the center of the base. 

 The periproct is large, acuminated on the upper margin, and placed in a broad, deep anal sulcus 

 that extends from near the apical system to the posterior margin. 



Belated forms. — Echinobrissus expansus has few points that would closely ally it with any 

 species of this genus hitherto described. 



ZocaZifo/.— Alabama or Mississippi. 



Geologic horizon. — Ripley formation, Upper Cretaceous. 



Collection. — Academy of Natural Sciences of Philadelphia (1465). 



Echinobrissus texanus Clark. 



Plate XXVIII, figures 2a-f. 



Echinobrissus texanus Clark, 1891, Johns Hopkins Univ. Circ, vol 10, No. 87, p. 76. 

 Echinobrissus texanus Clark, 1893, Johns Hopkins Univ. Circ, vol. 12, No. 103, p. 52. 

 Echinobrissus texanus Clark, 1893, U. S. Geol. Survey Bull. 97, pp. 62, 63, PL XXVI, figs. 2a-f. 

 Echinobrissus texanus Cragin, 1893, Geol. Survey Texas Fourth Ann. Rept., p. 150. 



Determinative characters. — Test ovate, rounded anteriorly, subquadrate posteriorly; upper 

 surf ace convex, apex forward of the center; base concave. Ambulacra lanceolate, subpetaloidal. 

 Apical system forward of the center. Peristome small, excentric. Periproct small, oval, in 

 narrow sulcus that begins some distance below the apical disk. 



Dimensions. — Length 18.75 millimeters; width 16.5 millimeters; height 9.5 millimeters. 



Description. — The single specimen of this species is somewhat damaged on the sides, so that 

 the ambital outline is not complete. It is ovate in form, broader posteriorly and subquadrate. 

 The upper surface is convex, but more or less compressed. The lower surface is concave. 



The ambulacra are narrowly lanceolate. The poriferous zones for a short distance from the 

 apical system are subpetaloidal in form. The posterior ambulacra are much longer than the 

 others, the unpaired ambulacrum being the shortest. The pores of each plate are oval and set 

 at an angle to one another. 



The interambulacral plates are large and covered with irreguarly arranged tubercles. 

 Between the tubercles a microscopic granulation covers the surface. 



The apical system is small and situated forward of the apex. The individual plates can not 

 be fully distinguished on the specimen examined. The peristome is apparently small, though 

 somewhat obscured. It is situated forward of the center of the base. 



The periproct is small, placed in a narrow sulcus that begins some distance posterior to the 

 apical system. 



Related forms. — Echinobrissus texanus is readily separated from E. expansus by its ovate 

 form and the shape and size of the anal sulcus. It is unlike any European species. 



Locality. — South bank of Colorado River, Austin, Tex. 



Geologic horizon. — Austin chalk, Upper Cretaceous. 



Collection.— U. S. National Museum (20266). 



