MAKYLAND GEOLOGICAL SURVEY 17 



Description. — The species was described from two lumbar vertebrae. 

 " They indicate both the smallest and the most slender species of the 

 genus. A section of the vertebrae would have an almost pentagonal 

 form, though the articular faces are sub-round, and, what occurs in no 

 other species, a little deeper than wide. The neural arch preserved in 

 elevated and possesses a weak pair of zygapophyses. The bases of the 

 broken diapophyses indicate that they are very wide. The lower face 

 of the centrum has a strong median longitudinal angle, stronger than 

 in any other species, and not prolonged into a keel. . . . The planes 

 of the centra are mostly straight." 



" Length centrum 1 in. 7.2 lines (39.4 mm.) 



Height 1 in. .5 lines (26 mm.) 



Width 1 in. .5 lines (26 mm.) 



Width neural canal 5.8 lines (11.6 mm.) 



Width basis diapophysis 10 lines (20 mm.) 



Height neural canal 6 lines (12 mm.) 



Height zygapophysis 8.2 lines (16.4 mm.)'" 



Cope, 18GS. 



Occurrence. — Calvert Formation. Charles county near the Patux- 

 ent river. 



Collection. — Philadelphia Academy of Natural Sciences. 



IXACANTHUS SPINOSUS CopC. 



Plate XIII, Figs. 2, 3a, 3b, 4. 



Friscodelphinus spinosiis Cope, 1868, Proc. Acad. Nat. Sci. Phila., vol. xx, pp. 187, 



188. 

 Priscodelphinus spinosus Leidy, 1869, Jour. Acad. Nat. Sci. Phila., vol. vii, p. 433 



(mention only). 

 Belosphys spinosus Cope, 1875, Proc. Amer. Philos. Soc, vol. xiv, p. 363. 

 Ixacanthus spinosus Cope, 1890, Amer. Nat., vol. xxiv, p. 603, fig. 1, p. 615. 



' Description. — The vertebrae are described as " about as broad as 

 long, with articular faces transversely oval and general form depressed; 

 sides of centrum nearly plane to a well marked obtuse median keel." 



