1890.] NATURAL SCIENCES OF PHILADELPHIA. 455 



Arcopagia Texana (rep. ^1. numismalis), Card'mm Sanctl Sabce (rep. 

 C. caiidatum), Avlcula convexo-plana (rep. A. anomala), Exogyra 

 Texana (rep. E. 3fafheroniana), and C'ljphosoma Texanum (rep. C. 

 tiara). Toxaster Texanus appeared to this observer to be the only 

 fossil indicative of a low horizon.^ 



The cumulative evidence that we have, thus tends to prove that 

 the Comanche beds of Texas occupy a horizon not lower than the 

 Cenomanian ; in other words, they are a part correspondent to what 

 some geologists recognize as the Middle Cretaceous, and what others, 

 who admit but two divisions in the formation, class as Upper Cre- 

 taceous. The}'^ are distinctly not Lower Cretaceous (or Neocomian) 

 and this lower member of the series has still to be found iu the 

 United States east of the Rocky Mountains.'^ The opposing evidence 

 of the single Echinoid, Toxaster, counts for little in this connection.* 



M. Virlet d'Aoust in a paper " Coup d'oeil sur la Topographic et 

 la Geologic du Mexique et de I'Amerique Centrale," mentions the 

 occurrence of a Hippuritic limestone, containing numerous Echin- 

 oids, near Tula, State of Hidalgo, about 40 miles north of the city 

 of Mexico.* Without doubt this is a portion of the limestone, rich 



^ Kreidebildungen von Texas, p. 18. 



~ Prof. Hill appears to have been, to a certain extent, misled in his correlation 

 of the Texas and Arkansas Cretaceous deposits through an unfortunate error 

 which is contained in Prof Whitfield's Report on the " Brachiopoda and Lamelli- 

 branchiata of the Raritan Clays and Greensand Marls of New Jersey" (Monogr. 

 U. S. Geol. Survey, 1885). It is there stated that Exogyra costala occurs only in 

 the "Lower Marl Beds" of the State (pp. XVIII, 41), and this assertion is ac- 

 cepted by Hill (A. J. Science, 1889, part 2, p. 472 — " Relations of the Uppermost 



^ Cotteau has recently described or recorded a number of Echinoids, from 

 various parts nf Mexico, which he considers lo be indicative of the Lower Creta- 

 ceous horizon (Bulletin Soc. Geol. de France, 1890, pp. 1^92-99 — Echinides Cre- 

 taces du Mexique). These are: Pseudocidaris Satisstcrei, from San-Juan Ray a, 

 in the State of Puebla; Salenia prestensis, from Guadalupe, Chihuahua; Eiiallas- 

 ter Mexicantis, from Guadalupe (Chihuahua) and Colima (Colinia); Diplopodia 

 {^Pseudodiadema) Malhosi, from Arivechi, .Sonora and Holecfypus Castilloi, from 

 Jalpa, Jalisco. The last named species is considered to represent either the Low- 

 er or the Middle Cretaceous. Pseudocidaris Saussurei occurs also in the deposits 

 of Tehuacan. and is the form which Nyst and Galeotti erroneously referred to Cid- 

 aris glandiferus of Goldfuss; the species is thus manifestly Upper Cretaceous. 

 Again, the so-called Diplopodia Malbosi, which is identified from two imperfect 

 specimens, both oC which differ in certain characters from typical representatives 

 of that species, is admitted to be " assurement voisine de Diplopodia variolaris'''' 

 (Cotteau, loc. cit., p. 294), which is also a distinctively Upper Cretaceous species. 



4 Bull. Soc. Geol. de France, 1866, p. 23. 



