152 
SELACHII. 
Ptychodus papillosus, E. D. Cope, Yert. Cret. Eorm. "West (U. S. 
Geol. Surv. Territ. 1875), p. 294.—Cretaceous; Colorado. 
Ptychodus triangularis , A. E. Reuss, Yerstein. bohm. Kreideform. 
1845, pt. i. p. 2, pi. ii. figs. 14-19. Teeth very doubt¬ 
fully placed iu this genus and referred to Acrodus by 
A. Eritseh, Kept. u. Eische bohm. Kreideform. 1878, 
p. 16, fig. 38.—Upper Cretaceous ; Bohemia. 
Ptychodus ivhipplefy, J. Mareou, Geol. IN’. America, 1858, p. 33, 
pi. i. fig. 4; J. Leidy, Extinct Yert. Eauna West Territ. 
(U. S. Geol. Surv. Territ. 1873), p. 300, pi. xviii. figs. 19, 
20; J. S. Newberry, Rep. Expl. Exped. from SantajjL 
to Colorado, 1876, p. 137, pi. iii. fig. 2^—Cretaceous 
(Niobrara Epoch); Colorado, Kansas, New Mexico, U.S.A. 
Y ith the Myliobatidse may also perhaps be associated the small, 
flattened, rhomboidal teeth from the E T pper Chalk of Maastricht, 
Holland, described under the name of Rhomhodus hinhhorsti ,1> 
1Y. Dames, Sitzungsb. Gesell. naturf. Ereunde, Berlin, 1881, p. 1. 
woodcuts. /) s , _ „ • 9 
?.l~ 
Family TRYGONIDiEh 
Pectoral fins uninterruptedly continued to, and confluent at, the 
extremity of the snout. Tail slender, sharply marked off from the 
disk. > Yertical fins absent or imperfectly developed, often re¬ 
placed by strong serrated spines. 
Genus TRYGONj Cuvier (“ ex Adanson ”), 
[Regne Animal, vol. ii. 1817, p. 136.] 
Genus TiRNITJRA, Muller & Henle. 
[Syst. Beschreib. Plagiost. 1841, p. 171.] 
The known fossil representatives of these two genera have not 
hitherto been exhaustively studied and described. Prof. Dr. Carl 
Hasse has made known 1 a detached vertebra, from the Lower 
Chalk (Aptian) of Dizier, considered to be referable to Trygon or an 1 
allied genus ; R. Lawley 2 has referred a Pliocene dermal tubercle 
to a species named T. targionii; and several nearly complete fishes, 
probably rightly placed here, have been discovered in the Middle 
Eocene limestone of Monte Bolca, near Yerona. One of the latter 
' Is atiirl. Syst. Elasmobr., Besom}. Tkeil, p. 144. pi. xix. figs. 4, 5, 6. 
Yuovi Sturli Pesci toss. Colline Toscane, 1876. p. 45, pi. ii. fig. 4, 
