■AKK] DIPLOPODIA TEXANUM. 49 



Cyphosoma tcxanum (Jablt, 1S5!>. Cat. Invert. I'os.sils, ("rctaeoons, p. 18. 



Cjiphonoma tcxatium (ijibb, 180}>. Calironiia Geol. Siiiv., Palf()iit()lo<;y, vol. 2, p. L'TtJ. 



I'seiidodiadcmn texamim Clark, 1S91. Jobu.s Ilopkius I ,'uiv(u-Kity ( 'ircnlars, No. 87, yi. 75. 



Detcrminatire characters. — Test larger subcireular; sides inflated; 

 iipixT surface elevated; lower suitiiec <lepressed, concave. .Vnibulacia 

 prominent, with two rows of primary tubercles; poriferous zones broad 

 above, narrow below; pores in siuj^ie pairs from i)cristome to ambitiis, 

 beyond wliieli to the apical disk they are bigeminal. Interambulacra 

 wide, witli four rows of primary tubercles at the ambitus, which become 

 reduced to tw^o at the poles. Mouth opening wide, about two-tifths 

 the diameter of the test. Discal oi)ening large, subpentagoiial. 



Diinennioiia. — Transverse diameter, 1;^ inches; iiiMght, ^ inch. • 



Description. — This species was tirst described by Roemer, in 1840, in 

 Texas, etc., as Diadcma /c.m»nw, but subsequently, in 1S52, referred to 

 Ci/phosoma. Although the perforated ma melons are not always shown 

 with di.stinctness at the flrst glance, they are suthcieutly numerous 

 upon careful inspection to warrant the removal of this form from the 

 genus Cyphosoma. 



The test is large, subcireular and elevated (PI. xv, Fig. Ic). The 

 sides are inflated, and the upper surface elevated and convex. The 

 base is depressed and concave. 



The aml)u]a('ral areas are broad and lanceolate. They have two rows 

 of primary tubercles, fourteen or fifteen in each series, that are large at 

 the ambitus and decrease gradually tOAvard the poles (PI. xv, Fig. Id). 

 A circle of scattered granules surround the narrow areolas. The porifer- 

 ous zones are broad upon the upi)er surface, but below the ambitus are 

 very much narrowed. The pores are in single pairs below the ambitus, 

 except directly at the mouth edges, where they becpme greatly increased, 

 as shown in Plate xvi, Fig. Iff. From the ambitus to the apical disk 

 they are bigeminal (PI. xv. Fig. Ir;), a character which Duncan, in his 

 recent revision of the Echinoidea, considers of generic importance and 

 sufficient ground for a separation of Diplopodia from Pseudodiadema. 



The interambulacral areas 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 (PI. xv. Fig. If), which become reduced to 

 two in the vicinity of the apical disk and mouth edges (PI. xvi, Fig. l/>, 

 Ic). In the center of the column the tubercles of the four rows are (jf 

 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 broad depression occurs 

 along the line of the central suture in the vicinity of the discal oi)ening. 



The mouth oi)ening is circular, but is broken by distinct incisions. 

 Its diameter is about two-fifths that of the test (PI. xv, Fig. 1^). 



The discal opening is large an<l subpentagonal (PI. xv, Fig. 1«). 

 Bull. 07-^1 



