CRICOIDS FROM THE UPPER CRETACEOUS OF 

 TAMAULIPAS, MEXICO. 



By Frank Springer. 

 Associate in Paleontology, United States National Museum. 



The crinoid stems described in this paper were submitted to me by 

 Dr. L. W. Stephenson, who collected them on two American-owned 

 ranches, known, respectively, as Chocoy and Las Flores (or Manuel), 

 on the line of the National Railways of Mexico, between Tampico 

 and Monterrey, in the State of Tamaulipas, Mexico. The circum- 

 stances of the discovery of these and other Upper Cretaceous fos- 

 sils are explained by Doctor Stephenson in Article 1 of this volume 

 of the Proceedings. 



These stem fragments apparently all belong to the genus Balano- 

 crinus, which ranges from the Jurassic to the Upper Cretaceous — a 

 form thus far known only by the stem, no other parts having yet been 

 found. Balanocrinus falls under the family Pentacrinidae, which is 

 characterized by a stem development far exceeding that of other 

 crinoids, attaining in the typical genus, Pentacrinus^ a length vari- 

 ously reported from 5 to 21 meters or 15 to 70 feet. These frag- 

 ments are evidently remnants of stems of similar vigorous growth, 

 as is indicated by the very large lateral cirri seen on some of them, 

 and confirmed by the fact that one specimen, about 25 cm. or 10 inches 

 long, is part of a stem which was traced in the rock for a distance of 

 about 5 meters or 16 feet. Balanocrinus is distinguished from the 

 more widely known Pentacrinus by the sculpturing of the joint faces 

 at the line of union of the columnals, which here takes the form of 

 crenelations around the outer edge of the joint face, and not along the 

 sides of the petaloid sectors into which the central part of the face is 

 divided. This character is thoroughly well marked in these speci- 

 mens, and by it the occurence of the genus is proved for the first 

 time in America to my loiowledge. The extreme development of 

 stem, although to be expected, has not before been so well shown in 

 this genus. 



Determination of species from the stem characters alone is unsatis- 

 factory, because, while a definite stem structure is recognized for the 

 genus, the minor details vary considerably in different parts of the 

 same stem, and we have no means of ascertaining whether any of 

 them are correlated with other characters so as to make them of spe- 



No. 2426-Proceedings U. S. National Museum, Vol. 61, Art. 5. 



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