54 MESOZOIO ECHINODERMATA OF THE UNITED STATES. [bull. 97. 



ten to twelve in eacb series (PI. xix, Fig", lo). These tubercles are eoii- 

 siderably larger than those of the ambulaeral area, and have wide 

 circular areolas, smooth bosses, and imperforate raanieloiis (PI. xviii, 

 Fig. 2c). On the base the tiil)ercles of all the areas are of nearly equal 

 size. The miliarj- si)ace is wnde, very nearly smooth in the upper por- 

 tions of the column, and sparsely covered with granules toward the 

 mouth edges. 



The apical disk is large and compact, the elongated genital plates 

 giving it a star-shaped appearance (PI. xviii. Fig. 2d). The well-de- 

 fined ocular plates, wedged into the interspaces, make the entire 

 outline subpeutagonal. Each genital plate is angular at the outer ex- 

 tremity and perforated. On the inner edge of the same there is a 

 semicircular depression, in the center of w^hich is a small niammillated 

 tubercle. 



The mouth opening is large, covering quite one-half the diameter of 

 the base. It is divided into ten lobes by ten shallow incisions (PI. xix, 

 Fig. Ih). 



Related forms. — This species shows many i)oints of similarity to 

 JEcMnus patagonensls, described by d'Orbigny in 1842, from the Tertiary 

 of southern Patagonia. The margin of d'Orbigny's species is sharper 

 and the apical disk of somewhat different shai)e. Moreover, if prop- 

 erly referred to the Tertiary, it is undoubtedly a different form. EcM- 

 nus (indhms, from the desert of Atacama, described by Philii^pi in 18G0, 

 is likewise closely allied to G. ZltteU, though more conical and present- 

 ing a different surface decoration of the plates. Ooniopygus major., 

 from the Cenomanian of Europe, is similar in many particulars, though 

 the pores are not increased around the peristome as in G. Zitteli, and 

 the apical disk is of more compact form. 



Locality and, geological horizon. — Goniopygna Zitteli is from the Ca- 

 prina limestone, a division of the Fredericksburg formation of the 

 Comanche series (lower Cretaceous), and has been collected at many 

 points in Texas, among others Spanish Oak branch, Williamson county, 

 and Round Rock. 



Collections. — U. S. National Museum: Texas Geological Survey. 



FiCIIINlB^. 



Test spheroidal. Ambulacra wide, with two or more rows of i)rimary 

 tubercles; poriferous zones usually trigeminal or polygeminal. Inter- 

 ambulacra witlf two or more row.? of primary tubercles, generally of 

 equal size with those of the ambulacra. Mouth opening large, decag- 

 onal. Apical disk composed of ten plates. 



