90 MESOZOIC AND CENOZOIC ECHINODERMATA OF THE UNITED STATES. 



Dimensions. — Length 22.5 millimeters; width 21.25 millimeters; height 15.5 millimeters. 



Description. — This small species has a broad, nearly flat upper surface, rising toward the 

 center, which is slightly elevated. The lower surface is rounded, sloping from near the center in 

 all directions. The sides are inflated. 



The ambulacra are unequal, the posterolateral pah being very short. The poriferous zones 

 are broad and shallow and but little depressed. The anterior ambulacrum is broad and shallow. 

 The surface is covered with small tubercles. The peripetalous f asciole is distinct. 



The peristome is email, only slightly depressed, and near the anterior margin. The peri- 

 proct is small and situated high on the truncated surface of the posterior margin. 



Locality. — Bexar County, Tex. 



Geologic horizon. — Washita group of the Comanche series, Cretaceous. 



Collection. — U. S. National Museum (8330). 



Hemiaster comanchei Clark, n. sp. 

 Plate XL VI, figures 2a-d. 



Determinative characters. — Test small to medium size, cordiform, high, lower surface flat, 

 sides inflated, apex forward of the center, peripetalous f asciole broad and clearly marked; ambu- 

 lacra rather narrow, depressed, petaloidal, the posterolateral considerably shorter than the 

 anterolateral, apical system nearly central; peristome near forward margin; periproct small,. 

 high on sloping posterior surface, showing clearly from above. 



Dimensions. — Length 25 to 60 millimeters ; width 22 to 50 millimeters; height 18 to 30 

 millimeters. 



Description. — The test of this species is small to medium sized, cordiform in ambital outline 

 and high. The upper surface is somewhat inflated, the lower surface nearly flat. The sides are 

 inflated.. The apex is forward of the center. 



The ambulacra are rather narrow and depressed, the poriferous zones petaloidal but narrow, 

 the posterolateral pair being considerably shorter than the anterolateral. The single anterior 

 ambulacrum in a broad, moderately depressed sulcus. The interambulacra are covered with 

 numerous irregularly scattered granules. The peripetalous fascioles are broad and distinct, with 

 granules scattered here and there over the surface. The apical system is nearly central on the 

 upper surface. The peristome is transversely ovate and near the forward margin. The periproct 

 is small, high on sloping posterior surface, and showing clearly from above. 



Related forms. — H. comanchei is the earliest of the Comanchean hemiasters and possesses 

 certain generalized features which suggest that it is the ancestral form from which H. whitei, 

 H. elegans, H. dalli, and H. calvini were derived. 



Locality. — Santa Monica Springs, bed of Colorado River, 10 miles west of Austin, Tex. 



Geologic horizon. — Glen Rose limestone of Trinity group, Comanche series, Cretaceous. 



Collection. — Johns Hopkins University (T 3012). 



Hemiaster dalli Clark. 



Plate XL VII, figures la-f. 



Hemiaster dalli Clark, 1S91. Johns Hopkins Univ. Circ, vol. 10, No. 87, p. 77. 

 Hemiaster dalli Clark, 1893, Johns Hopkins Univ. Circ, vol. 12, No. 103, p. 52. 

 Hemiaster dalli Clark, 1893, U. S. Geol. Survey Bull. 97, p. 89, PI. XLVIII, figs. 2a-e. 



Determinative characters. — Test cordate, subhexagonal, depressed; upper surface with 

 sharp ridges between the ambulacral furrows; base flat; sides rapidly declining; anterior margin 

 deeply grooved. Ambulacra unequal, very deeply depressed on petaloidal portions; antero- 

 lateral pair much bent in upper part. Peristome oval, situated on vertically truncated surface 

 of posterior margin. 



Dimensions. — Length 45 millimeters; width 45 millimeters ; height 21 millimeters. 



