50 MESOZOIC AND CENOZOIC ECHINODERMATA OF THE UNITED STATES. 



is situated before the periproct and occupies the center of the disk. The periproct is subellipti- 

 cal, rounded anteriorly, angular posteriorly, and slightly elevated at the border. 



The adoral surface is flat and the peristome large, covering nearly one-half the diameter of 

 the test. The peristome is circular, with ten incisions upon the edge that divide it into nearly 

 equal sized lobes. 



Related forms. — Credner in discussing the affinities of this form considers it to be closely 

 related to Salenia petalifera Def ranee and S. desori Wright. It is somewhat more elevated than 

 S. petalifera, the radial ridges on its apical system are more pronounced, and its ocular plates 

 enter more compactly into the composition of its disk. From S. desori, on the other hand, it 

 differs more widely, both in the character of the test plates and the decorations of the apical 

 system. With S. scutigera Gray it shows some points in common. 



Localities. — Cileola, Comanche spring (figured specimen A) ; Bosque County _ (figured speci- 

 men B); 2\ miles north of Denison; 5 miles west of Kent; Bexar County; Round Rock; Wil- 

 liamson County, Tex. 



Geologic horizon. — Fredericksburg and Washita groups of the Comanche series, Cretaceous. 



Collections. — U. S. National Museum (8329, A); Boston Society of Natural History; Johns 

 Hopkins University (T3003, B). 



Salenia tumidula Clark. 



Plate XIII, figures la-j. 



Salenia tumidula Clark, 1891, Johns Hopkins Univ. Circ, vol. 10, No. 87, p. 75. 

 Salenia tumidula Clark, 1893, Johns Hopkins Univ. Circ, vol. 12, No. 103, p. 51. 

 Salenia tumidula Clark, 1893, U. S. Geol. Survey Bull. 97, pp. 41, 42, PI. XI, figs. la-j. 

 Salenia tumidula Johnson, 1905, Acad. Nat. Sci. Philadelphia Proa, vol. 57, p. C. 



Salenia tumidula Weller, 1907, Cretaceous paleontology of New Jersey : Geol. Survey New Jersey, pp. 282, 283, PL VIII, 

 figs. 1-10. 



Determinative characters. — Test small, subglobose; outline of upper surface regularly convex. 

 Ambulacra narrow, nearly straight, with two rows of mammillated granules between the pore 

 pairs; poriferous zones slightly flexed; pores uniserial. Interambulacra wide, composed of two 

 alternating rows of five or six plates. Apical system large, regularly convex, subcircular; 

 periproct slightly elevated. Peristome small. 



Dimensions. — Diameter 2 to 13 millimeters; height 1 to 10 millimeters. 



Description. — The perfectly preserved specimens of this beautiful species permit determi- 

 nation of all the details of structure. 



The general form of the test is subglobose. The sides are inflated and regularly curved, 

 rising into a convex upper surface, from which the periproct projects but slightly. The lower 

 surface is almost flat and toward the peristome is slightly depressed. 



The ambulacra are rather broad, increasing in width from the apical system to the peristome. 

 Extending along the center of each area are two rows of mammillated granules, 15 or 16 in each 

 row, between which are other minute granules. The poriferous zones are narrow and nearly 

 straight; the pores round, regularly arranged in a uniserial series, and largest in the middle 

 of the column. 



The interambulacra consist of two rows of alternating plates, five or six in each row. The 

 larger tubercles diminish rapidly in size toward the mouth edges, and are very indistinct on the 

 plates bordering the same. Each areola is large and circular, the boss crenulated, and the mame- 

 lon flattened and imperforate. The miliary space is bordered with oval granules of irregular size 

 and arrangement, although most numerous between the rows of tubercles. The sutures of the 

 plates are very indistinctly marked. 



The apical system is prominent, subcircular, with a regularly curved convex surface, from 

 which the anal aperture projects but slightly. The granular decorations of the surface often 

 coalesce and appear as broken ridges extending radially from the five openings in the genital 

 plates. The periproct is oval, slightly pointed below, and projects but slightly above the level 

 of the apical system. It is bordered by a flangelike edge that is formed of the anal and two 

 genital plates. 



