ON THE FOSSIL GENUS POROCYSTIS, CRAGIN. 1 



MAY M. JARVIS. 



Under the name of Porocystis pruniformis F. W. Cragin de- 

 scribed in 1892, in the Fourth Annual Report of the Geological 

 Survey of Texas, curious spherical forms from the Cretaceous of 

 Texas. In regard to the geological levels at which they were 

 collected, he states : " In chalky limestones of the alternating 

 beds in Travis, Burnet, Williamson, Lampasas and other counties, 

 associated with Serpula, small Ostreidae, and other forms indic- 

 ative of moderate depth of water. In the Third Annual Re- 

 port of the Survey, Mr. Taff has also recorded it from rocks of 

 the Fredericksburg division of the Hickory-Cow Creek divide, 

 Travis County, associated with several fossils of the Exogyra 

 Texana beds." 



Cragin considered that these fossils were Bryozoa, and speaks 

 of having sent some to the late Dr. Ferdinand Roemer, who re- 

 turned them marked " ? Parkeria, sp. nov." His figures of them 

 are not detailed, and for this reason as also because they are 

 evidently not Bryozoa, a new description seems called for. There 

 is a large series of specimens in the University Museum, the 

 greater number considerably eroded but some with the surface 

 sculpturation well preserved. 



The tests are more or less prolate spheroids, sometimes one 

 axis much shorter than the other. At one point on the surface 

 is a flattened, very slightly protuberant area, free of any sculp- 

 turation, which might represent either the point of attachment of 

 a stalk, or have been a large foramen. For various considera- 

 tions it is probably the latter, so that the* whole fossil proper 

 would be a hollow spheroid with very thin shell and with a large 

 opening at one end. The interior of each fossil is a mass of 

 structureless limestone. This flattened area, or foramen as it 

 may preferably be called, is usually upon the edge or very near 

 it, when the specimen is much flattened, but in one of such cases 

 it is in the center of the flat side. Canals radiate from the fora- 



1 Contributions from the Zoological Laboratory of the University of Texas, no. 70. 



388 



