ci.AKK] CIDAKIS WALCOTTI. 37 



Avliilt^ toward l)oth jij)ical disk and niontli oiK'niiii;- Micy aiv rcdiu-ed to 

 two, Incynlaiiy scattered anumg the rows of granules are others 

 smaller in size. The pores are oval and separated by transverse ele- 

 vations that partially eneircle the openings, leaving a depression 

 between each pair (IM, vii, Fig. Ir). 



The iuteranibulaeral ])lates are wide and bear large circular tuber- 

 cles (Tl. VII, Fig. Id). The areola of each tubercle is radially ridged, 

 deei)ly depressed, and surrounded by a row of nuiuimilated granules. 

 The boss is slightly elevated above the level of the i)late, and presents 

 a smooth and sharp ridge around tlie small perforated mamelon (PI. Vij, 

 Fig. le). The miliary space is wide and thickly set with small elevated 

 granules of equal size. The apical disk and mouth edges are lacking. 



Related forms. — At first sight this species shows strong- points of 

 similarity with C. seejHi-i/era Mantell from the White Chalk of England, 

 although the arrangement of granules in the ambulacral area is differ- 

 ent. The areola of G. sceplrifera is described as smooth, while that of 

 C. texanus is clearly ridged radially. The only related form reported 

 from Texas is Leiocidaris hemigranosus, formerly referred to Cidaris, btit 

 which, as will be shown, does not l)elong" to that gemis. Cidaris Bran- 

 neri, from Brazil, described by White, is allied to G. texanitSj although 

 presenting differences in the character of the areola and arrangement 

 of granules in both the ambulacral and iuterambulacral areas. 



Locality and f/eologieal horizon. — This form is found in the Washita 

 formation of the Comanche series (lower Cretaceous) of Bexar county, 

 Texas. 



GoUection. — U. S. National Museum. 



Cidaris Walcotti Clark. 



Plate VI, Figs. 4a-rt 



Cidaris Walcotti Clark, 1891. Johns Hopkins University Circulars, No. 87, p. 75. 



Determinatire characters. — Test small, inflated. Ambulacral areas 

 narrow, sinuous, with four rows of granules between the depressed 

 poriferous avenues. Iuterambulacral areas broad; each tubercle with 

 depressed circular areola, smooth boss and small imperforate mamelon. 

 Miliary space wide, thickly covered with small granules. 



Dimensions. — -JBeight, 1 inch (1). Width, 1^ inches ( ?). 



Description. — The fragments of this form examined are sufficiently 

 <listinctive to separate it from other species. A nearly complete iuter- 

 ambulacral area, with the adjoining ambulacra, shows that the test of 

 tlu' species is small and in a marked degree inflated (PI. vi, Fig. 4«). 



The ambulacral areas are narrow, slightly sinuous, and provided with 

 four nearly equal rows of granules between the poriferous avenues (PI. 

 VI, Fig. -ic). At times additional granules are irregularly inter.spersed. 

 The poriferous avenues themselves are narrow, deeply depressed, and 

 slightly sinuous. The pores are round, with funnel-shaped openings, 



