60 MESOZOIC AND CENOZOIC ECHINODEBMATA OP THE UNITED STATES. 



Related forms. — The species is not unlike C. texanum, from which, however, it is separated by 

 its smaller size, subpentagonal form, and two instead of four rows of primary tubercles. 

 Locality. — Austin, Tex. 



Geologic horizon. — Austin chalk, Upper Cretaceous. 

 Collections. — U. S. National Museum (S311); Johns Hopkins University. 



Cyphosoma texantjm Roemer. 



Plate XXI, figures la-g. 



Diadema texanum Roemer, 1849, Texas, p. 392. 



Cyphosoma texanum Roemer, 1S52, Die Kreidebildungen von Texas, p. S2, PI. X, fig. 6. 



Cyphosoma texanum Conrad, 1857, in Hall's U. S. and Mex. Boundary Survey Rept., vol. i, pt. 2, p. 145, PI. I, fig. 3. 



Phymosoma texanum Desor, 1858, Synopsis des echinides fossiles, p. 90. 



Cyphosoma texanum Gabb, 1859, Cat. Invert. Fossils Cretaceous, p. 18. 



Cyphosoma texanum Gabb, 1869, Geol. Survey California, Paleontology, vol. 2, p. 276. 



Pseudodiadema texanum Clark, 1891, Johns Hopkins Univ. Circ, vol. 10, No. 87, p. 75. 



Diplopodia texanum Clark, 1893, Johns Hopkins Univ. Circ, vol. 12, No. 103, p. 51. 



DiplopodiatexanumCUA, 1893, U. S. Geol. Survey Bull. 97, pp. 47, 48, PI. XV, figs, la-f; PI. XVI, figs, lar-d. 



Cyphosoma texana Aguilera, 1893, Datos para la geologia de Mexico, p. 26. 



Diplopodia texana Cragin, 1893, Geol. Survey Texas Fourth Ann. Rept., p. 149. 



Diplopodia texanum Cragin, 1894, Colorado Coll. Studies, vol. 5, p. 47. 



Cyphosoma texana Aguilera, 1897, Inst. geol. Mexico Bol., Nos. 4, 5, and 6, p. 21. 



Diadema texana Bose, 1899, Inst. geol. Mexico Bol., No. 13, p. 11. 



Cyphosoma texana Bose, 1899, Inst. geol. Mexico Bol., No. 13, p. 11. 



Determinative characters. — Test large, subcircular; sides inflated; upper surface elevated; 

 lower surface depressed, concave. Ambulacra prominent, with two rows of primary tubercles; 

 poriferous zones broad above, narrow below; pores uniserial from near peristome to ambitus, 

 beyond which to the apical system they are biserial. Interambulacra wide, with four rows of 

 primary tubercles at the ambitus, which become reduced to two at the pores. Peristome wide, 

 about two-fifths the diameter of the test. Periproct large, subpentagonal. 



Dimensions. — Diameter 15 to 20 millimeters; height 8 to 20 millimeters. 



Description. — This species was first described by Roemer in 1S49 as Diadema texanum, but 

 subsequently, in 1852, was referred to Cyphosoma. 



The test is large, subcircular, and elevated. The sides are inflated and the aboral surface 

 elevated and convex. The base is depressed and concave. 



The ambulacra are broad and lanceolate. They have two rows of primary tubercles, four- 

 teen or fifteen in each series, that are large at the ambitus and decrease gradually toward the 

 poles. A circle of scattered granules surrounds the narrow areolas. The poriferous zones are 

 broad upon the upper surface, but below the ambitus are very much narrowed. The pores are 

 uniserial below the ambitus except directly at the peristome, where they become greatly in- 

 creased. From the ambitus to the apical system they are biserial. 



The interambulacra are about one and one-half times the width of the ambulacral at the 

 ambitus. There are four rows of primary tubercles at the ambitus which become reduced to two 

 in the vicinity of the apical system and peristome. In the center of the column the tubercles of 

 the four rows are of about equal size, but those of the outer rows become much more rapidly 

 reduced in size toward the poles. Small secondary tubercles are found on the outer margin of the 

 plates, while irregularly scattered granules cover the space between the tubercles. A slight 

 depression occurs along the line of the median suture. 



The peristome is circular, but is broken by distinct incisions. Its diameter is about two- 

 fifths that of the test. The periproct is large and subpentagonal. 



The species was incorrectly referred earlier by the author to Diplopodia. A more thorough 

 study of the much better material now available shows that this form is a Cyphosoma. 



Belated forms. — The species is very closely related to if not identical with C. volanum of the 

 Washita group, but is somewhat taller and its four rows of primary tubercles on each interam- 

 bulacrum are rather more definitely developed even on small specimens. It also shows a less 



