CKETACEOUS ECHINODERMATA. 45 



Cidaris texanus Clark. 

 Plate IX, figures 2a-i'. 



Cidaris texanus Clark, 1891, Johns Hopkins Univ. Circ, vol. 10, No. 87, p. 75. 



Cidaris texanus Clark, 1893, Johns Hopkins Univ. Circ, vol. 12, No. 103, p. 61. 



Cidaris texanus Clark, 1893, U. S. Geol. Survey Bull. 97, pp. 36, 37, PL VII, figs. la-e. 



Determinative characters. — Test large, inflated. Ambulacra narrow, sinuous, with four rows 

 of granules between the poriferous avenues, which at the ambitus are increased to six and toward 

 the apical system and peristome are reduced to two rows. Pores oval, separated by transverse 

 elevations, which partially envelop the openings. Interambulacra wide, with large circular 

 tubercles. Areola circular, depressed; boss smooth; mamelon small, perforated. Miliary space 

 wide, covered with numerous small granules. 



Dimensions. — Diameter SO millimeters ( ?) ; height 40 millimeters ( ?). 



Description. — A large portion of the test of this beautiful species is excellently preserved. 

 All of the characteristic features, except those relating to the apical system and peristome, 

 are clearly shown. The test, however, is somewhat compressed, so that the original form can 

 not be made out with certainty. The ambulacral areas are narrow and slightly flexuous. 

 Between the poriferous avenues, which are narrow and depressed, are four rows of granules of 

 nearly equal size, which directly at the ambitus are increased to six, and toward both apical 

 system and peristome are reduced to two. Irregularly scattered among the rows of granules 

 are others smaller in size. The pores are oval and separated bj r transverse elevations that 

 partly encircle the-openings, leaving a depression between each pair. 



The interambulacral plates are wide and bear large circular tubercles. The areola of each 

 tubercle is radially ridged, deeply depressed, and surrounded by a row of mammillated granules. 

 The boss is slightly elevated above the level of the plate and presents a smooth and sharp ridge 

 around the small perforated mamelon. The miliary space is wide and thickly set, with small 

 elevated granules of equal size. The apical system and peristome are lacking. 



Related forms. — At first sight the species shows strong points of similarity to C. sceptrifera 

 Mantell from the White Chalk of England, although the arrangement of granules in its ambula- 

 cra is different. The areola of C. sceptrifera is described as smooth, and that of C. texanus as 

 clearly ridged radially. The only related form reported from Texas is Leiocidaris hemigranosus, 

 formerly referred to Cidaris, but which, as will be shown, does not belong to that genus. Cida- 

 ris branneri, from Brazil, described by White, is allied to 0. texanus, but differs from it in the 

 character of the areola and the arrangement of granules in both the ambulacral and interam- 

 bulacral areas. 



Locality. — Bexar County, Tex. 



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



Collection. — U. S. National Museum (8381). 



Cidaris walcotti Clark. 



Plate IX, figures 3a-d. 



Cidaris walcotti Clark, 1891, Johns Hopkins Univ. Circ., vol. 10, No. 87, p. 75. 

 Cidaris walcotti Clark, 1893, Johns Hopkins Univ. Circ, vol. 12, No. 103, p. 51. 

 Cidaris walcotti Clark, 1893, U. S. Geol. Survey Bull. 97, pp. 37, 38, PI. VI, figs. 4a-d. 

 Cidaris walcotti Johnson, 1905, Acad. Nat. Sci. Philadelphia Proc, vol. 57, p. 6. 



Cidaris walcotti Weller, 1907, Cretaceous paleontology of New Jersey: Geol. Survey New Jersey, pp. 281-282, PL VII, 

 figs. 10-13. 



Determinative characters. — Test small, inflated. Ambulacral areas narrow, sinuous, with 

 four rows of granules between the depressed poriferous avenues. Interambulacral areas broad; 

 each tubercle with depressed circular areola, smooth boss and small imperforate mamelon. 

 Miliary space wide, thickly covered with small granules. 



Dimensions.— Type specimen: Height about 25 nhlhnieters; width about 37.5 millimeters. 

 39800°— 15 i 



