42 MESOZOir ECHTNODER^tATA OF THE UNITED STATES. [bull. 97. 



])cscription. — The perfectly preserved specimens of tliis beautiful 

 species admit of a determination of all the d(?tails of structure. 



The general form of the test i.s subglobose. The sides are inflated 

 and regularly curved, rising into a convex upper surface, from which 

 the anal opening projects but slightly (PI. xi. Fig-. Ic). The lower sur- 

 face is quite flat, and toward the mouth opening slightly depressed. 



The ambulacral areas are rather broad, increasing in width from the 

 apical disk to the mouth edges (PL xi. Fig. 1/). Extending along the 

 center of each area are two rows of mammillated granules, fifteen or 

 sixteen in each row, between which are other minute granules. The 

 X)oriferous zones, are narrow and nearly straight; the iiores round, 

 regularly arranged in a unigeminal series, and largest in the middle of 

 the column. 



The interambulacral areas consist of two rows of alternating plates, 

 five or six in each row (PI. xi. Fig. Id). The larger tubercles diminish 

 rai)idly 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 mamelon flattened and imperforate (PI. xi. Fig. Ij). 

 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 jjlates are very indistinctly marked. 



The apical disk is prominent, subcircular, with a regularly ciTrved con- 

 vex surface, from which the anal aperture projects but slightly. The 

 granular decorations of the surface often coalesce and appear as broken 

 ridges extending radiall}' from the five opening.s in the genital plates 

 (PI. XI, Fig. Ig). The anal opening is oval, slightly pointed below, and 

 l)rojects but slightly above the level of the apical disk. It is bordered 

 by a flange-like edge that is formed of the anal and two genital plates. 



The mouth opening is small, occupying scarcely two-fifths of the diam- 

 eter of the test. Ten incisions divide the edge into lobes, the ambu- 

 lacra! lobes projecting the farther (PI. xi, Fig. 1/). 



Related fornifi.— The identity of this species is readily established by 

 the straight poriferous zones and peculiar decorations of the apical 

 disk. The number of mammillated granules in the ambulacral areas is 

 less than in S. te.rana, while the oval granules of the interambulacral 

 areas are readily distinguishable from the round forms of S. helluJa. 



The anal aperture also projects far tess than in *S'. texana, although 

 in this respect it is not unlike S. hellula. 



Locality and fleolof/ical horizon. — This species is from the yellow lime- 

 stone of the middle marl bed (upper Cretaceous) of Timber creek. New 

 Jersey. 



Collection. — Philadelphia Academy of Natural Sciences; Johns Hop- 

 kins University 



