346 MAURICE G. MEHL 
posteriorly. Not much can be said of the arch except that it is 
apparently low, the diapophyses arising just above the centrum. 
The diapophyses are rather stout, directed outward in a horizontal 
plane, and have an oval cross-section the greater diameter of which 
is directed in an antero-posterior direction. The centra vary 
between 33 mm. and 4o mm. in length and are but slightly wider 
than long. Of the fifteen caudal vertebrae present two are from 
the posterior region and are disklike, cylindrical, and flattened on 
the articular surfaces. The other thirteen caudals are more 
anterior in position, from round to oval with flattened ventral 
surface in cross-section, moderately biconcave, the lateral surface 
concave antero-posteriorly. The diapophyses arise low down on 
the centrum nearly on a plane with the ventral surface and directed 
out and downward. The lower articular borders are slightly 
beveled for the chevrons. In length the centra range between 
21 mm. and 26 mm. and from 33 mm. to 36 mm. in width. 
The left pectoral paddle, with the exception of the ulna, a super- 
numerary mesopodial, a supernumerary epipodial, perhaps, and a 
few phalanges, is excellently preserved. A comparison of the 
paddle of this species with that of Muraenosaurus leedsi Seeley 
(Figs. ra and 10) shows the similarity of these two forms. The 
humerus is relatively long and slender, the shaft is oval in cross- 
section, tapering gradually from the distal expansion nearly to the 
proximal extremity. Here it expands sharply on the inner radial 
side into the head with a similar but less sharp expansion on the 
opposite side of the shaft. A broad shallow grove on the inner and 
outer sides of the shaft separates these two expansions into head 
and tuberosity which lie in a plane twisted at an angle of about 
forty degrees with that of the distal expansion. Along the upper 
third of the radial margin of the shaft there is a well-marked ridge, 
which loses its identity, however, in a short distance both proxi- 
mally and distally. About 65 mm. below the head there is a strong 
ridge, for the attachment of muscles, running up and backward on 
the inner surface of the shaft. The distal end is moderately ex- 
panded and shows articular facets for the radius and ulna, the former 
measuring over half the width of the expansion, the latter a little 
less than one-third. Although there is no facet for the articulation 
