'■'-Ar.KO LEIOCIDAKIS 1IKMI(!KAN0SUS. 3!) 



from whicli il is sci)iiViito(l by the presence of I'lirrows uiiitiiift- \ho jxnes 

 oreiich pair. In this respect it is a typical representative of tlie <;enns 

 Leiocldayis of Besor. A very jjood ilhistratiou is giveu by Dr. White 

 in the Twelftli Aninfal Report for 1878 of the IT. S. Geological and (leo- 

 graphical Snrvey of the Territories, althongh necessarily, from the size 

 oi'the figiire, the furrows connecting the i)ores are not very distinctly 

 shown. This species is the hxrgest echinoid known from the Texas 

 Cretaceous, and, with possibly a vsingle exception, the lai-gest from the 

 American Mesozoic. In one unusually fine specimen obtained from 

 Prof. R. T. Hill the test is subspherical, although considerably broader 

 and more flattened on the oral than aboral side.^ 



The ambulacral areas are narrow and sinucnis, with six rows of gran- 

 ules between the poriferous avenues (1*1. vii. Fig. 2/>). The regular 

 aiTangement of the granules is not persistent, the number being in- 

 creased irregularly near the middle of the column and somewhat reduced 

 toward the apical disk and the luouth opening. The i)oriferoiis avenues 

 are wide and deeply depressed, the pores of eacli pair being united 

 by a shallow furrow. 



The interambulacral areas are wide and the plates of massive size 

 (PI. VII, Fig. 2rt). The tubercles occupy the center of the plates and 

 are large and prominent. The areolas are deeply depressed, subcircu^ 

 lar or slightly polygonal, and occupy more than half of the greatest diam- 

 eter of the i)lates. On all the specimens examined the areolas show 

 perfectly smooth surfaces, although Shumard mentions the occurrence of 

 radiating ridges. Toward the center each areola rises to form the boss, 

 which is provided marginally with a sharp smooth ridge. The mam- 

 elon is large, subspherical, with a dee.]) perforation upon its summit (PI. 

 ^11, Fig. 2c). The miliary space is wide and covered with large, irreg- 

 ularly-shaped and flattened granules, some round and some oval in form. 

 Interspersed among these are much smaller grannies, which increase in 

 number along the margin of the plates. The apical disk and mouth 

 edges are wanting. 



Related forms. — This species is readily separated from any hitherto 

 described from American or Euro])ean strata. Its characters are well 

 defined and distinctive. 



Locality and geolof/ical liorhon. — Shumard says that it is found '' in the 

 AVashita limestone fComanche series (lower Cretaceous)], forming the 

 upper part of the Bluff of Red river, Lamar county, and 10 miles above 

 the mouth of Kiamesha creek, at both localities associated with Ostrea 

 (jiiadriplieata.^'' This places it in the Denison beds. It has only been 

 reported from Texas. 



CoUeetions.—U. S. National Museum; Prof. R. T. Hill. 



• A much more perfect specimen (PI. IX, Figs, la-c) has been examined by the writer since the above 

 ilescription was prepared. 



