Weno and Pawpaw Formations 99 



plates. Comptonia elegans on the other hand has a central ridge of very 

 rounded elevated plates running the length of each ray and connecting 

 to form on the disk a central, narrow, elevated ring. In our species the 

 center of the disk is flat and the plates are very little disarranged, since 

 the depression mentioned above has not disturbed the relations of the 

 central plates to each other. 



Calliderma and Nymphaster differ from our species in many notable 

 features. Both have the aboral interadial areas in most species confined 

 to the disk, so that the supero-and infero-marginal plates meet over most 

 of the length of the ray. This is not true in the Texas species. Both 

 genera named were described from recent species, the genotypes being 

 Nymphaster protentus Sladen 1 and Calliderma emma Gray. 2 



This species differs from Comptonia elegans Gray in several important 

 respects. The disk is practically flat in our species; it, however, shows 

 some evidence of flattening in preservation, since the central plates are 

 considerably and abruptly depressed below the level of the supero-marginal 

 plates. Comptonia elegans, on the other hand, has a central ridge of very 

 rounded elevated plates running the length of each ray and connecting 

 to form on the disk a central narrow elevated ring. In our species the 

 center of the disk is flat and the plates are very little disarranged, as the 

 foregoing description shows. 



PENTACEROS AMERICANUS n. sp. 

 PI. 7, figs. 1-3 



MEASUREMENTS: R (average of two) 45.0 mm. 



r (average of five) 10.4 mm. 



R:r 4.33:1 



A species having the form of Pentaceros jurassicus Quenstedt and in 

 most respects agreeing with the described generic characters, is here re- 

 ferred to this genus. 



HORIZON: Base of the Pawpaw formation, clay fades, 

 TYPE LOCALITY: 714, one-fourth mile south of the International 

 and Great Northern Railway bridge across Sycamore Creek, four and 

 one-half miles southeast of Fort Worth, Texas. One individual, the type, 

 was found here. 



Sladen: Narrative of Challenger Exp., 1886, vol. 1, p. 612; Zool. Chal. Exp., part li, 

 Report on the Asteroidea, 1889, p. 294. 



Fisher, W. K., Starfishes of the Philippine seas and adjacent waters. U. S. N. M. 

 Bull. 100, vol. 3, p. 261, 1919. 



2 Gray: Proc. Zool. Soc. Lond., part XV, 1847, p. 76; Ann. Mag. Nat. Hist., 1847 

 vol. XX, p. 198; Synopsis of Species of Starfish, British Museum, 1886, p. 7. 



