CHOCTAW AND GRAYSON TEllRANES OF THE ARIETINA. 45 

 FAUXA OF THE GRAYSOX ^fARLS (AND MARLY LIMESTONES). 



Cyphosoma volanum. Crag. Modiola pedernaUs, Roem. 



Holaster completns. Crag. Curdium{Protocard.)texanuin,Con. 



Holaster nanus, Crag. Roudairia denisonensia. Crag. 



Holaster sitjiermis, Crag. Tapes deiitonensis, Crag. 



Eiiallastei- iiiflatus. Crag. Cyprimevia texana, Roem. 

 Epiastev hemiasterinus, Crag.* Homomya washita. Crag. 



Ostrea perversa, Crag. Turritelta seriatim-gramdaia, R. 



Gryphcea mucronata, Gabb. TurriteUa denisonensis. Crag. 



Exogyra arietina, Roem. Nautilns texanus, Shum. 



Exogyra drakei, Crag. Turrilites brazosensis, Roem. 



Lima icacoensis, Roem. . Sphenodiscus ji^dernalis, Roem. 



Vola texana, Roem. Hoplites texainis. Crag. 

 Avicula dispar. Crag. 



The Grayson fauna, like the Choctaw, is much poorer in 

 southern Texas than in northern. The more common forms 

 occurring in it in Travis county are, in the writer's experience, 

 the following: 



Ostrea 2>erversa, Vola texana, 



Gryphcea mucronata, Plicatula dentonensis. Crag. 



Exogyra arietina. 



Hill has recorded from the beds of this terrane at Austin, 

 the following also: Terehafella ivacoensis, Roem, Diplo podia 

 texanum, Roem, Protocdvdium texanum, Con., PncJiymya 

 austinensis, Shum., and Asiarie robbinsi, White; in case of 

 the first and last, only a single example of each. 



In both northern and southern Texas, the Grayson marl 

 is especially characterized by that peculiar form of Gryphsea 

 that, by Hill, TaflP, and other recent authors, has usually been 

 regarded as a variety of G. pitcheri, Morton, and has been 

 called by Taff, " the Vola phase of G. pUcheri,'''' but has re- 

 cently been recognized by Hill as the truly distinct G. mu- 

 croncda, Gabb. 



* This name has priority over that of " Hemiaster calvini," a name subsequently 

 applied to the species by Clark, whose specimens are " from the Shoal creok lime- 

 stone .... in Travis county." Owing to the feeble development of tlie peripeta- 

 lous fasciole, the writer referred this species to the genus Epiaster it being, in fact, 

 intormodiato between that genus and Hemiaster iu tlio one important character that 

 distinguislies these genera. Since, however, the peripetalous fascit)le is present, 

 though imperfoctly, and in some specimens very imperfectly, developed, it would 

 probal)ly be more consistent to refer the species to Hemiaster, as Clark has done. 

 But if tliis 1)0 done, it is (juestionable whether the same generic disposition 

 should not also be made of the well known " Epiuster " elegaiia, Shum, wliich, in the 

 most perfectly preserved examples, ie also seen to have a feebly developed peripeta- 

 lous fasciole. 



