NO. 1519. MOR OS A IJR US A GILLS RED ESCRIBED— GILMORE. 161 



ties, the writer should judge from Hatcher's figures and description, 

 are not present in the axis of Dlplodocvs^ and tliey also appear to be 

 absent in the axis of 21. grandis. (See fig. 6.) 



The anterior ventral surface of the centrum is abruptly truncated 

 transversely, forming a broad, flat facet for the intercentrum of the 

 axis. This element, so far as the writer has been able to ascertain, 

 has never before been found in a member of the Opisothocoelia. In 

 older individuals it may coalesce with the centrum and thus lose its 

 identity. However, many of the sutures one would expect to find 

 distinct in this individual have become entirely obliterated. The 

 specimen of 31. grand!!< described and figured by Marsh, which, 

 according to the figures given, is a very much larger individual, 

 shows sutures between the centra and spinous processes of the verte- 

 brae. Yet in this very much smaller specimen there is no indication 

 whatever of their union. So it would appear, as 

 inferred by Marsh in his original description, that 

 this is an adult representing the most diminutive 

 member of the genus. 



The second intercentrum (see fig. lA.r. In.) is 

 a small rectangular block of bone of greater width 

 than length and of medium thickness, being 

 thicker in front than behind. The posterior bor- 

 der is straight and fits closely to the truncated 

 ventral surface of the centrum. It thus occupies 

 a primitive position, as found in Platecarpus, and 

 forms a liplike proiection. An examination of fi«.7.-ventkalviewof 



" I ' _ AXIS OF MOROSAURUS 



Marsh's figure of the axis of 3£. grandis would agilis (Cat. no. 5384), 

 indicate that it also bore an intercentrum, but in il^J'^^^^:J^''^I:'^':lT. 



' TERCENTRUM OP AXIS; 



that case probably became completely co-ossified p. s(/r/, posterior zyga- 

 with the centrum. (See fig. 6^.) the anterior ^r^^..^™^^^" 

 border is gently convex transversely. This ele- 

 ment occupies the excavated surface of the centrum and does not 

 extend below the lower surface. It is 22 mm. wide and 14 mm. long. 



From the posterior and superior borders of the neural arch two 

 diverging postzygapophysial lamina rise. These extend upward and 

 backward until the postzygapophyses are reached; above them they 

 continue upward and forward, meeting anteriorly and superiorl}^, 

 forming the prespinal lamina. Thej^ thus inclose a deep postspinal 

 cavity which opens posteriorly and superiorly. Prominent rugosities 

 are developed just above the postzygapophyses. These also appear 

 to be present on the axis of Morosaurm grandis. 



A transverse process is developed on the anterior sides of the neural 

 arch. It is moderately broad and thin and is directed downward, 

 backward, and outward, terminating in a rounded end. The hori- 

 zontal lamina extends from the transverse process to the postzygapo- 

 Proc. N. M. vol. xxxii— 07 11 



