10 MESOZOIC AND CENOZOIC ECHINODERMATA OF THE UNITED STATES. 



The stelleroicls contain representatives of both the Ophiuroidea and the Asteroidea, the 

 genera Ophioglypha, Astropecten, Goniaster, Pentagonaster, and Pentaceros being found. The 

 material comes from widely separated areas in New Jersey, Texas, and Wyoming. 



The echinoids are very numerous, both the regular and irregulay types being well repre- 

 sented. Both the Lower and Upper Cretaceous deposits of Texas contain many species and vast 

 numbers of individuals at several horizons ; and the Upper Cretaceous of the Atlantic and eastern 

 Gulf coasts, particularly in New Jersey, North Carolina, Alabama, and Mississippi, although 

 fully characterized by its echinoid fauna, affords many forms. The western interior and 

 Pacific coast Cretaceous contains a much smaller representation of echinoid types. 



Among the Lower Cretaceous genera represented, more particularly in Texas, are: Cidaris, 

 Salenia, Hypodiadema, Goniopygus, Pseudodiadema, Diplopodia, Cyphosoma, Holectypus, 

 Pyrina, Enallaster, and Hemiaster. Outside of Texas very few Lower Cretaceous echinoids 

 have been recognized. The Horsetown formation of California contains a few forms. 



The Upper Cretaceous of Texas contains a large echinoid fauna and some of the genera 

 possess many species. They are: Cidaris, Leiocidaris, Leptarbacia, Orthopsis, Heterodiadema, 

 Cottaldia, Diplopodia, Cyphosoma, Micropsis, Holectypus, Echinobrissus, Cassidulus, Anan- 

 chytes, Cardiaster, Holaster, and Hemiaster. 



The Upper Cretaceous of the Atlantic and Gulf coasts has afforded representatives of the 

 following genera: Cidaris, Salenia, Pseudodiadema, Coptosoma, Psammechinus, Echinobrissus, 

 Trematopygus, Botriopygus, Cassidulus (many species of which have been recognized), Catopy- 

 gus, Echinanthus, Ananchytes, Cardiaster, Hemiaster, and Linthia. Much the larger number 

 of Atlantic coast forms have been found in the New Jersey Cretaceous, especially in the Vincen- 

 town sand of the Eancocas group, which is regarded as probably of Danian age. The western 

 interior and Pacific coast areas contain few representatives of the echinoids, most of the species 

 belonging to the genus Hemiaster. 



The absence of species identical with those of other continents and particularly of Europe 

 renders impossible a detailed correlation of American and foreign horizons on the basis of their 

 echinoderm faunas. However, genera represented in the main divisions of the Mesozoic in 

 America are with scarcely an exception similar to those typical of the same divisions elsewhere. 



The accompanying tables show the stratigraphic positions of the more important American 

 Mesozoic formations, the geologic distribution of the Mesozoic Echinodermata of the United 

 States, and the stratigraphic distribution of the Cretaceous Echinodermata of Texas. 



