1377.] 195 [Cope. 
The third type is smaller in all its dimensions, and the crown is equal to 
the root in long diameter. In my single specimen the distal portion of 
the crown is lost; the part which remains exhibits neither contraction 
nor expansion of outline. The borders are very obtuse, and each surface 
resembles a roll inwards which is bounded by a shallow parallel groove on 
the inner face of the tooth. Between the grooves the surface is slightly 
convex. The section is thus an oval with one side very little convex. The 
enamel is thick and marked with longitudinal rugosities. 
Measurements. M. 
EM CMOMALAP MIEN 1. ch cnw we meine amselevicdice oswedcneses  .OO0 
Sic “CML EIER Rev le PRE ene et ae OTe Cae came 12350) 
ATC Bee Bete ciate a inidd. Solucous ameyeinairaiesieaaewis oe» SOLE 
longitudinal.......... .01385 
Diameter of crown at middle ' % 
NRIeRensoeccoenoce allishy 
TICHOSTEUS LUCASANUS, gen. et sp. nov. 
Char. gen.—The characters of this genus are derived primarily from the 
vertebre. They are nearly amphiplatyan, but one extremity of the articu- 
lar face is slightly concave, while the other is still more slightly convex 
or concave. The borders of the former are expanded, while those of the 
latter are not enlarged. The centrum is hollow, but the chamber does not 
communicate with the external medium by a lateral foramen, asin Camara- 
saurus. The neural arch is attached by suture. There is no capitular ar- 
ticulation on the centrum. 
Char. specif.—There is no hypapophysis on either dorsal or lumbar ver- 
tebree preserved, and the surface is smooth excepting some delicate longi- 
tudinal ridges extending to the border of the expanded extremity. The 
narrower extremity of a dorsal vertebra is nearly round and presents a 
slight median tuberosity ; the opposite end is wider than deep, and its sur- 
face is uniform. The smaller extremity of a lumbar vertebra is slightly 
concave. 
Measurements. M. 
loneitudinal. 2.22). -s.0-) see 
Diameter of dorsal centrum 2 vertical......<...-.--+- 020 
igo Meiseinneasooauscane  olse 
Width of base of neural arch with diapophysis........ .010 
This species is dedicated to its discoverer, O. W. Lucas, of Canyon City, 
Colorado, the Superintendent of the Public Schools of the surrounding re- 
gion. Through the scientific interest and energy of this gentleman the ex- 
tinct vertebrata of the Dakota division of the Cretaceous Period hitherto un- 
known to science are being brought to light. The care and skill exercised 
by Mr. Lucas in the preservation of remains, which are often bulky, and 
always fragile, deserve the thanks of all students of this department of 
science. 
